Ahyi seamount is one of a long string of submarine seamounts at the northern edge of the Northern Mariana Islands, part of the Mariana Back-arc segment of the Izu-Bonin trench in the western Pacific Ocean. The remote location of the seamount has made eruptions difficult to document, but seismic stations installed in the region confirmed an eruption in the vicinity in 2001. No further activity was reported until a new eruption was detected by seismic stations and felt by divers in the immediate area in April 2014. Volcanic activity in the Commonwealth of the Northern Mariana Islands is monitored by the US Geological Survey's Volcano Hazards Program, and observations are sometimes gathered by NOAA (National Oceanic and Atmospheric Administration) expeditions. The 2014 eruption and follow-up observations from December 2014 are summarized here.

The eruption at Ahyi seamount between 24 April and 17 May 2014 (BGVN 39:02; Haney et al., 2014) was first recorded as T-phase signals that were detected by various seismometers in the Mariana Islands. Submarine explosions were also heard and felt by NOAA scuba divers conducting coral reef research on the SE coastline of Farallon de Pajaros (Uracas) Island, about 20 km NW of Ahyi. In the same area, the NOAA crew reported sighting mats of orange-yellow bubbles on the water surface that extended up to 1 km from the shoreline. T-phase seismic signals registered across the Northern Mariana Islands (NMI) seismic network at a rate of approximately 10 per hour until 8 May, and then sporadically until 17 May (Haney et al., 2014).

During mid-May, the NOAA ship Hi'ialakai gathered multibeam sonar bathymetry and took three water-column CTD casts (Conductivity, Temperature, and Depth sensor; it gives scientists a precise and comprehensive charting of the distribution and variation of water temperature, salinity, and density). The May 2014 bathymetry revealed that the minimum depth to the summit was about 90 m, notably deeper than the 60 m measured during a 2003 survey. In addition a new crater about 100 m deep had formed at the summit, replacing the summit cone. Also, a distinct landslide chute descended the SE slope 2,300 m, removing material from the head and depositing debris at the base (see figure 4, BGVN 39:02). Significant particle plumes were detected with all three CTD casts, indicating ongoing hydrothermal activity. Plumes with optical anomalies up to 0.4 NTU (nephelometric turbidity units) were found S and W of Ahyi at 100-175 m water depth, corresponding to the depth of the new summit crater. NTU's are light backscattering measurements done by optical sensors in sea water to determine the presence of hydrothermal plumes in the water column.

On 4 December 2014, the NOAA Expedition "Submarine Ring of Fire 2014 – Ironman" visited Ahyi, and again used a CTD sensor to assess the hydrothermal status of the volcano. EM122 multibeam bathymetry data imaged CO₂ gas bubbles rising from the summit (figure 5), and clearly revealed the new summit crater. When the CTD sensor and sampling package was lowered into the water, it measured a thick plume of particles indicating ongoing hydrothermal activity near 150 m depth, close to the base of the new crater that formed during the eruption in April-May 2014.

Figure 5. Three-dimensional image of the summit of Ahyi submarine volcano gathered on 4 December 2014 with the mid-water data shown above the new crater created by the April 2014 eruption. The summit crater is ~100 m deep. CO2 bubbles (in green) can be seen rising from most of the summit, suggesting that there is more than one source of venting. This image shows an area 850 m across with depths ranging from 78 (red) to 400 m (blue). No vertical exaggeration. Image courtesy of Submarine Ring of Fire 2014 - Ironman, NSF/NOAA (http://oceanexplorer.noaa.gov/explorations/ 14fire/logs/december04/media/ahyi.html).

References: Haney, M. M., Chadwick, W., Merle, S. G., Buck, N. J., Butterfield, D. A., Coombs, M. L., Evers, L. G., Heaney, K. D., Lyons, J. J., Searcy, C. K., Walker, S. L., Young, C., and Embley, R. W., The 2014 Submarine Eruption of Ahyi Volcano, Northern Mariana Islands, American Geophysical Union, Fall Meeting 2014, abstract V11B-4727.

Geologic Background. Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the sea surface about 18 km SE of the island of Farallon de Pajaros (Uracas) in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area of the seamount, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations.

Information Contacts: National Oceanic and Atmospheric Administration (NOAA), Office of Ocean Exploration and Research, 1315 East-West Highway, Silver Spring, Maryland, USA (URL: http://oceanexplorer.noaa.gov/welcome.html); US Geological Survey, Volcano Hazards Program (USGS-VHP), 12201 Sunrise Valley Drive, Reston, VA, USA (URL: https://volcanoes.usgs.gov/index.html).

Russia's Alaid volcano, located just off the southern tip of the Kamchatka Peninsula, is the northernmost of the chain of volcanoes that comprise the Kuril archipelago. A number of strong explosive eruptions have been recorded there in the last 200 years, including VEI 4 explosions in 1790 and 1981. The last eruption occurred between 5 October and 12 December 2012 when repeated thermal anomalies and ash plumes from the summit crater were observed. A new eruption was first reported on 29 September 2015 by the Tokyo Volcanic Ash Advisory Center (VAAC) (BGVN 41:06). Alaid is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT); valuable information about this remote site is also gathered from satellite thermal infrared data reported by both the University of Hawai'i's MODVOLC system and the Italian MIROVA system.

A new eruption at Alaid was reported on 29 September 2015. It was characterized by strong thermal anomalies and intermittent gas-and-ash plumes. The thermal anomalies were interpreted by KVERT as Strombolian eruptions and lava flows. The first episode of the eruption exhibited strong thermal anomalies with only two reports of ash, and lasted until 4 January 2016. The second episode began with the reappearance of a strong thermal anomaly and an ash plume on 20 February 2016. This was followed by a series of low-level ash plumes in March and April, and ongoing strong thermal anomalies through early May. The anomalies decreased during mid-May and June, but then a large spike of intense anomalies in the first week of July was accompanied by ash plumes and observations by KVERT of Strombolian eruptions at the summit crater and a lava flow down the SW flank. Thermal activity decreased substantially following this spike, and tapered off completely by the second week of August 2016.

The Tokyo VAAC reported an eruption at Alaid at 2120 UTC on 28 September (0720 on 29 September local time) 2015. They reported it as below 6.1 km altitude, and volcanic ash was not identifiable in satellite images. KVERT raised the Aviation Color Code from Green to Yellow early on 2 October 2015 (local time) based on an intense thermal anomaly observed during the night that they interpreted to be the beginning of a new Strombolian eruption. The first thermal anomalies identified by MIROVA (Middle InfraRed Observation of Volcanic Activity) also appear during the first two days of October (figure 5). MODVOLC thermal alerts first appeared on 5 October and were essentially continuous with no more than a few days break until 4 January 2016. The MIROVA signal remained steady until about the same date when it abruptly decreased. KVERT reported consistent and usually intense thermal anomalies, when the volcano was not obscured by clouds, until 4 January. They observed anomalies in satellite images with decreasing frequency and intensity during the rest of January and into early February.

Figure 5. MIROVA thermal anomaly data for Alaid from 5 April 2015 through 13 January 2017. The first thermal anomaly is visible on 1 or 2 October 2015. The signal remained consistently in the Moderate to High range until the first week of January when it abruptly stopped. It reappeared during the third week of February and was consistently 'High' until mid-May when it decreased to 'Low' values. A sudden spike to near 'Very High' values during the first week of July corresponded with KVERT reports of Strombolian eruptions from the summit crater and a lava flow down the SW flank. Courtesy of MIROVA.

The first report of observed gas-and-steam activity (after the Tokyo VAAC report on 29 September) was by KVERT on 16 December. Visual observations from nearby Paramushir Island (45 km SE) noted a small amount of ash in the steam-and-gas plumes on 28 and 29 December. The Tokyo VAAC also reported a plume of volcanic ash at 4.6 km altitude on 29 December drifting SW. On 5 February 2016 local time KVERT lowered the Aviation Color Code (ACC) to Green, noting decreased thermal activity and only moderate continuing fumarole activity during the previous weeks. A break in the thermal activity between early January and late February is also recorded in the MIROVA data (figure 5).

Another eruptive episode began with the appearance of a strong thermal anomaly and a weak ash emission sending a plume 50 km E on 20 February UTC, leading KVERT to raise the ACC back to Yellow. Renewed MIROVA thermal anomalies appeared on 16 or 17 February (figure 5). The first MODVOLC thermal alert was reported 23 February, and they were essentially continuous (except for probable cloudy days) until 5 May 2016. MIROVA thermal anomalies values remained consistently in the 'High' (VRP of 10⁸-10⁹ Watts) range until the second week of May when they dropped back to 'Low' (VRP of 10⁶-10⁷ Watts).

KVERT reported gas-and-steam plumes containing a small amount of ash on 20 and 24 February 2016. Minor ashfall (less than 1 mm) was reported on 24 February in Severo-Kurilsk, 45 km SE on Paramushir Island. The Tokyo VAAC also reported a possible eruption that day with a plume to 3 km altitude extending NE. An ash plume was reported by KVERT and the Tokyo VAAC on 3 March 2016 at 3 km altitude drifting 52 km WSW. This prompted KVERT to raise the ACC to Orange. Ash emissions continued for the next two days, rising to 3.4-3.9 km and drifting S and SW, according to the Tokyo VAAC. KVERT reported visual data from Paramushir Island confirming an ash plume extending SW on 6 March, and satellite data showing the plume 90 km SW that same day.

Possible eruptions were again reported on 11 and 12 March 2016 by the Tokyo VAAC under 3 km altitude, and on 12 and 14 March by KVERT as visual observations from Paramushir extending 85 km E. Weak ash emissions were reported several more times in March and April rising to between 3 and 4.3 km altitude and drifting in various directions (some as far as 90 km) on 22, 26, and 30-31 March, and 1, 9, 14, 18, 21, and 24 April. KVERT noted that on 21 and 23 April the ash plumes extended about 260 km SE. Moderate thermal anomalies were reported by KVERT from mid-May through the beginning of July, and MIROVA anomalies registered in the 'Low' range during this time. KVERT reported on 12 May that satellite data showed a lava flow on the SW flank. They noted continuing thermal anomalies over the volcano during clear weather throughout May and June, but no ash plumes were reported.

KVERT and the Tokyo VAAC once again noted ash plumes that drifted 150 km SW during 3-4 July. This is consistent with an Aura/OMI image of an SO₂ plume drifting SW from Alaid on 4 July (figure 6). On 7 July, KVERT reported Strombolian activity from a new cinder cone in the summit crater and a lava flow effusing down the SW flank. A sudden spike in the MIROVA data with values rising to 10⁹ W of Radiative Power during 3-7 July (figure 5) corroborates the KVERT observation of the lava flow; the MODVOLC data also shows a strong signal between 3 and 7 July, including several alert pixels on the SW flank of the volcano (figure 7).

Figure 6. SO2 plume drifting SW from Alaid captured on 4 July 2016 by the Aura instrument on the OMI satellite. Courtesy NASA/GSFC.

Figure 7. MODVOLC thermal alert pixel data for Alaid during 3-7 July 2016 showing a multi-pixel alert at the summit likely from Strombolian activity and alert pixels on the SW flank described by KVERT as a lava flow. Green grid lines represent 0.05 decimal degrees. Courtesy of MODVOLC.

The last ash plume was observed by the Tokyo VAAC on 3 July 2016. The final thermal alert was recorded by MODVOLC on 7 July. MIROVA anomalies continued steadily, however, at low levels through the first week in August before ceasing. Two additional MIROVA anomalies appeared briefly in the first and last weeks of September. KVERT reported thermal anomalies continuing until early August. They also noted a gas-and-steam plume extending 155 km NE on 26 July. In their VONA (Volcano Observatory Notice for Aviation) issued on 11 August 2016 at 2305 UTC (1105 on 12 August KST), KVERT lowered the ACC to Yellow based on decreasing intensity of thermal anomalies, and no additional ash plumes since 4 July; they lowered it again to Green on 19 August (local time) citing no further evidence for volcanic activity since the last thermal anomaly on 11 August.

Geologic Background. The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/ ); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/ ); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/, http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: http://so2.gsfc.nasa.gov/index.html).

Large lava flows descend the flanks of Alaska's Cleveland volcano, located on Chuginadak Island in the Aleutians, slightly over 1,500 km SW of Anchorage (figure 18). However, dome growth and destruction by frequent small ash explosions have been more typical behavior in recent years; historical activity, including three large (VEI 3) eruptions, is recorded back to 1893. The Alaska Volcano Observatory (AVO) and the Anchorage Volcanic Ash Advisory Center (VAAC) are responsible for monitoring activity and notifying air traffic of aviation hazards associated with Cleveland. This report summarizes activity between July 2011 and June 2014, and provides details of activity from June 2014 through February 2017.

Figure 18. Morning sunlight illuminates the southeast-facing slopes of the Islands of the Four Mountains on 15 November 2013 in this photograph taken from the International Space Station (ISS). The islands, part of the Aleutian Island chain, are the upper slopes of volcanoes rising from the sea floor: Carlisle, Cleveland, Herbert, and Tana. Carlisle and Herbert volcanoes are distinct cones and form separate islands. Cleveland and the Tana volcanic complex form the eastern and western ends respectively of Chuginadak Island; clouds obscure the connecting land area. Astronaut photograph ISS038-E-3612 acquired with a Nikon D3S digital camera using a 400 mm lens, provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center. The image was taken by the Expedition 38 crew. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. Caption by William L. Stefanov, Jacobs at NASA-JSC. Courtesy of NASA Earth Observatory ( http://earthobservatory.nasa.gov/IOTD/view.php?id=82588).

Summary of activity during July 2011-June 2014. Dome growth and destruction characterized activity at Cleveland during 2011-2014. Eruptive episodes are challenging to determine due to weather conditions and the remoteness of the volcano; detectible ash plumes are intermittent, and thermal anomalies caused by dome growth are often obscured in satellite imagery. Seismic and infrasound data on explosions often provide valuable information. Dome growth was clearly documented between late July and October 2011 (BGVN 36:08, 37:01). An ash cloud observed on 29 December 2011 was followed by observations of dome growth in satellite data on 30 January 2012. Significant ash explosions occurred during April and June 2012 (BGVN 38:10). AVO also reported ash plumes on 12 July and 20 August 2012. Another small ash cloud was noted by AVO on 10 Nov 2012.

Details of the 2013 activity are provided in Dixon et al. (2015) and summarized here. Elevated temperatures in mid-January 2013 were followed by observations of a new lava dome that measured 100 m in diameter on 30 January 2013, and a second lava extrusion on 9 February. Elevated surface temperatures were intermittently observed until the next ash explosion on 4 May 2013, which was followed by a larger series of explosions on 6 May that filled the crater with tephra and created flowage deposits on the NE, E, and SE flanks. On 26 July, analysis of a satellite images suggested a new lava flow within the summit crater.

From August through 28 December 2013 the infrasound and seismic networks detected a number of additional explosions and periods of infrasonic tremor (see table 8 in Dixon et al., 2015). Most of these events did not have an accompanying ash signal in AVHRR satellite images, suggesting minor to no ash emissions. A detectible ash cloud on 30 December 2013 was preceded by strongly elevated surface temperature readings in the summit area on 28 December (BVGN 39:08). Ash plumes were again detected at the summit on 2 January, 25 February, and 6 March 2014. Cleveland was quiet for almost three months until an explosion on 5 June with a weak ash signal was detected.

Summary of activity during June 2014-February 2017. The growth and explosive destruction of six lava domes at Cleveland were recorded between June 2014 and February 2017. Although an explosion on 5 June 2014 was the last recorded explosion with confirmed ash until 14 June 2015, thermal and visual satellite evidence suggested dome growth activity during July-September and late November 2014. Weakly elevated surface temperatures at the summit were intermittent through February 2015. Minor ash deposits on the flanks were observed on 14 June 2015 in addition to stronger elevated surface temperatures, suggesting a new dome growth episode. An explosion on 21 July 2015 was thought to have destroyed the dome, and strongly elevated surface temperatures indicating new dome growth continued through July and August.

Moderately-elevated surface temperatures were detected at the summit in satellite data from January through 16 April 2016 when a new explosion was recorded. Satellite views in late April indicated that the August 2015 lava dome had been replaced with a small cinder cone within the summit crater. Explosions with no ash reported occurred twice in May, before the extrusion of a small amount of lava forming a new lava dome was observed on 17 May 2016, and which continued to grow for about one week. Moderately-elevated surface temperatures reappeared in mid-July, and field crews observed incandescence in a vent at the summit in late July. Satellite thermal anomalies were persistent from mid-May through September 2016. A new explosion on 24 October 2016 destroyed the dome emplaced in May; satellite views in November showed a deep pit within the summit crater. Weakly elevated surface temperatures reappeared in early December 2016. Moderately-elevated surface temperatures reappeared on 31 January 2017, preceding an explosion on 3 February; satellite observations after this indicated that a new dome of similar size to earlier ones was once again filling the summit crater.

Activity during June 2014-February 2015. An ash-bearing explosion occurred in the late evening hours of 5 June 2014, resulting in a detached cloud with a weak ash signal observed in a satellite image that rapidly dissipated; no additional ash explosions were observed over the next 12 months. Weakly elevated surface temperatures were observed in satellite data on 7 July, and a vigorous steam-and-gas plume was observed on 8 and 9 July. Typical steam-and-gas emissions and persistent elevated surface temperatures in the summit crater were noted in satellite observations during clear periods through July and August, but AVO received no reports from pilots or mariners of any eruptive activity. Scientists working on the island in early August noted incandescence and puffing activity of steam and gas at the summit, and witnessed several small rockfall events. A newly installed webcam and other geophysical equipment at station CLCO near Concord Point on the SE coast of Chuginadak Island, about 15 km E of the volcano's summit, became operational in September 2014. In mid-September several rockfall signals were detected by the new local seismic network, and indicated the continued instability of volcanic debris on the steep upper flanks of the volcano.

Elevated surface temperatures were observed at the summit on clear days with occasional minor steaming visible in webcam images from late September to late October 2014. On 14 November AVO reported that vigorous steaming from the summit crater was observed in webcam images during the prior week, although they remarked that steam emissions are routinely observed at Cleveland and do not necessarily indicate an increase in unrest. On 28 November, they noted that a small mound of lava in the crater was observed in clear satellite views earlier that week that may have corresponded with the appearance of a faint thermal signal in the satellite data; the lava possibly extruded around 24 November. Satellite views on 19 December 2014 showed weakly elevated surface temperatures at the summit vent.

Low-density gas emissions and weakly elevated surface temperatures in the summit region were observed on 1 January 2015, and during clear weather up to 9 January. After this, nothing of note was observed in satellite or webcam images, and no significant activity was detected in seismic or infrasound (air pressure) data until weakly elevated surface temperatures were again detected in satellite data on 25 February. A low-level steam-and-gas plume emanated from the summit on 24 February, and again was identified in multiple satellite images on 28 February. During March, April, and May 2015, no significant activity, except for occasional steaming from the summit crater, was observed during periods of clear weather, causing AVO to downgrade both the Aviation Color Code (ACC) and the Volcano Alert Level (VAL) to Unassigned on 28 May 2015.

Activity during June 2015-March 2016. AVO issued a new VONA (Volcano Observatory Notice for Aviation) on 17 June 2015 returning the Aviation Color Code to Yellow (Yellow is 2nd lowest on a 4-color scale), and the Volcano Alert Level to Advisory (also 2nd lowest on a 4-level scale). This was based on satellite detection of elevated surface temperatures at the summit and an image from 14 June showing very minor ash deposits on the upper flanks. They interpreted the increase in temperature as consistent with renewed growth of the small lava dome within the crater. Elevated summit surface temperatures were again observed on 30 June, and during three clear days in early July. On 21 July AVO detected an explosion in both infrasound and seismic data, and raised the ACC to Orange and the VAL to WATCH. Satellite views were obscured by clouds, though a dusting of ash on the upper flanks was noted by a nearby field crew and recorded by the webcam later in the day. The explosion destroyed the dome that had formed in November 2014. Strongly elevated surface temperatures were recorded at the summit during the last week of July, including a thermal alert pixel from the MODVOLC system on 31 July.

Slightly elevated surface temperatures were recorded at the summit during the first week of August 2015. On 4 August, a field crew working in the area reported a small amount of lava covering the crater floor. Surface temperatures of the cooling lava measured by the crew were in the range of 550-600°C. Minor ash-and-gas emissions were also observed. A small explosion occurred on 6 August at 2203 AKDT, but no ash cloud was identified. Strongly elevated surface temperatures suggestive of lava effusion were noted in satellite data through 18 August, and weakly elevated temperatures were recorded for the rest of August and September. A small swarm of earthquakes was detected on 29 August.

AVO lowered the ACC to Yellow and the VAL to ADVISORY on 14 October 2015, citing the likely cessation of lava effusion, while minor steaming, weakly elevated surface temperatures, and slightly above-background seismicity continued through November 2015. Exceptionally clear weather during late November allowed many views of the volcano, showing only modest steaming from the summit. Elevated surface temperatures were detected twice during December, and an increase in frequency of small VT (Volcano-Tectonic) events was noted on 22 and 23 December, but otherwise no significant seismicity or emissions (other than steam plumes) were detected.

Moderately-elevated surface temperatures were detected at the beginning of the second week in January 2016, followed by several small earthquakes per day during the third week, and weakly elevated temperatures. Low-level seismicity and elevated surface temperatures were next observed during the last week of February; a brief burst of small local earthquakes was recorded on 28 February followed by weakly elevated surface temperatures during the first week of March. Moderately-elevated surface temperatures were again observed during the last week of March.

Activity during April-September 2016. A new explosion on 16 April 2016 was detected in both infrasound and seismic data, but satellite views were obscured by clouds. AVO raised the ACC to Orange until 29 April, when they noted that recent satellite imagery indicated that the August 2015 lava dome had been replaced with a small cinder cone within the summit crater; seismic activity remained lower after the explosion. Another explosion on 5 May at 1844 local time led AVO to raise the ACC back to Orange, although no ash emissions were observed above the cloud deck. A brief explosive event on 10 May was detected by pressure sensors near the volcano, and again no ash was reported.

A small volume of lava was extruded from the summit on 17 or 18 May, as confirmed in satellite data. The low-relief, 50-m-diameter dome was similar in size and shape to the ten domes observed since 2011, the most recent of which was extruded and destroyed earlier in May. During the week of 20 May, this lava dome enlarged to about 60 m in diameter. Dome growth appeared to have paused or ceased by 23 May. Weakly elevated surface temperatures were observed in mostly clear views by satellite on 25 and 26 May, which is consistent with the presence of the new lava dome. The Aviation Color Code was lowered from Orange to Yellow by AVO on 3 June when no other signs of eruptive activity were observed. Occasional clear satellite views detected weakly elevated surface temperatures that AVO interpreted as consistent with cooling lava during June 2016.

The MIROVA infrared data suggests ongoing thermal anomalies from late May through September 2016 (figure 19). AVO reported weakly-to-moderately-elevated surface temperatures reappearing during the second and third weeks of July. Field crews conducted an overflight during the last week of July and observed incandescence from a vent in the summit crater. Low-level steam plumes and minor degassing were observed a number of times during August. A small swarm of earthquakes occurred on 29 August; owing to the small number of telemetered seismometers on Cleveland, the locations and magnitudes of the earthquakes could not be determined precisely. Thermal anomalies were observed in satellite data during the last week of August and slightly elevated surface temperatures were observed on clear satellite images a number of times in September.

Figure 19. MIROVA data from 18 January 2016 to 18 January 2017 showing a persistent thermal anomaly from Cleveland starting about the time of the observation of the new lava dome (17 or 18 May) through late September 2016. A new thermal anomaly appears in late December 2016. AVO reported elevated surface temperatures on 6 January 2017. Courtesy of MIROVA.

Activity during October 2016-February 2017. AVO detected an explosion at 1310 local time on 24 October 2016 that was heard by residents in Nikolski (75 km E), prompting AVO to raise the ACC to Orange and the VAL to WATCH. No evidence of an eruption cloud was detected above the weather cloud present at 8.5 km altitude, and no ashfall was reported in Nikolski. However, clear post-explosion webcam views of the volcano showed a darkened area around the summit crater which may have been the result of minor ash fallout. Narrow dark streaks were also observed extending down the upper snow-covered part of the edifice, which according to AVO may have been produced by small flows of meltwater and ash. They lowered the ACC back to Yellow on 4 November 2016. Satellite views from early November indicated that the lava dome emplaced in late May was mostly destroyed in the 24 October explosion, and was replaced with a deep pit within the summit crater. Minor steaming was observed from the summit during a few periods of clear weather in November.

Observations of weakly-elevated surface temperatures returned 8 and 9 December, with minor steaming at the summit observed on clear days. A MIROVA thermal anomaly signal reappeared around 25 December. This was followed by AVO's observation of weak-to-moderate elevated surface temperatures during first week of January 2017. Low-level steam plumes were seen on clear days later in the month. Moderately-elevated surface temperatures appeared in satellite data on 31 January. A new explosion on 3 February 2017 led AVO to raise the ACC to Orange. Satellite observations indicated that a new lava dome had been extruded and was partially filling the summit crater. The new dome was about 70 m in diameter and similar in size to previous lava domes that have developed on the floor of the crater.

References: Dixon, J.P., Cameron, C., McGimsey R.G., Neal, D.A., and Waythomas, C., 2015, 2013 Volcanic activity in Alaska-Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2015-5110, 92 p., http://dx.doi.org/10.3133/sir20155110 .

Geologic Background. Beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited, dumbbell-shaped Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Cleveland is joined to the rest of Chuginadak Island by a low isthmus. The 1730-m-high Mount Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name for Mount Cleveland, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845(URL: http://www.ssd.noaa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

Daikoku seamount lies in the Northern Seamount Province of the Mariana Arc, and is about 850 km due N of Guam in the western Pacific Ocean. The summit is about 325 m below sea level and was first shown to be hydrothermally active in 2003 (figure 3). NOAA (National Oceanic and Atmospheric Administration) has conducted four expeditions to the Northern Mariana Islands in 2003, 2004, 2006, and 2014 under their Ocean Explorer program, specifically to study the volcanoes and the marine life they support. A comparison of the bathymetry recorded in 2003 and 2014 suggests that an explosion may have occurred at Daikoku during that interval, and both geochemical data and rock sampling indicate ongoing hydrothermal activity. In 2016, a research cruise conducted by the Schmidt Ocean Institute included a visit to Daikoku that revealed sulfur chimney formation.

Figure 3. Bathymetry and other data gathered on the 2003 NOAA Ocean Explorer Program's 'Submarine Ring of Fire 2003' expedition at the Mariana Arc between 9 February and 5 March 2003. The stars indicate submarine volcanoes where evidence of hydrothermal activity was found. The volcanoes were mapped in high resolution, and sampled with a CTD, as indicated by the open black circles on the tracklines. The red dots represent the location of the deployed hydrophones and the red line represents the location of the back-arc spreading center. Daikoku is located in the Northern Seamount Province of the Mariana Arc. Courtesy of NOAA's 'Submarine Ring of Fire 2003' expedition.

Geochemical sampling of the seawater is carried out with an instrument package that measures conductivity, temperature, and depth, commonly referred to as a CTD. Turbidity of the water, which estimates the concentration of particulate matter suspended in the plumes, is also measured. The CTD carries bottles for seawater sampling which is then geochemically analyzed.

On 15 April 2004 the NOAA 'Submarine Ring of Fire 2004' expedition made a single dive at Daikoku and noted warm water present over large areas of sandy sediment deposits near the summit, and small flatfish in great abundance in the venting areas. The 'Submarine Ring of Fire 2006' expedition again visited Daikoku on 4 May 2006 and discovered a "cauldron" of molten sulfur (BGVN 31:05). They also observed extensive sulfur crusts in the vicinity of the cauldron, suggesting past emissions of liquid sulfur; they were able to sample a large piece of sulfur crust (figure 4). At that time, they also mapped two large craters on the summit. One pit was reported as over 100 m deep and about 80 m in diameter, and a large plume of white fluid was observed rising out of it.

Figure 4. Sulfur crusts near the Diakoku "cauldron" were observed insitu as well as sampled by the ROV. Upper Image: Sulfur crusts in the vicinity of the sulfur cauldron (BGVN 31:05) imply past emissions of liquid sulfur at Daikoku. Lower Image: The Jason remotely operated vehicle (ROV) holds up a large piece of the sulfur crust that was sampled at Daikoku on 4 May 2006. The lasers- two red dots in the images- are 10 cm apart. Courtesy of Submarine Ring of Fire 2006 expedition, NOAA Ocean Explorer Program.

Researchers from the NOAA Ocean Explorer program visited Daikoku again on 14 December 2014 during its 'Submarine Ring of Fire 2014 – Ironman' expedition, which was conducted from the R/V (Research Vessel) Revelle between 29 November and 22 December 2014. They gathered geochemical and bathymetric data which they were able to compare with 2003 data. The CTD information gathered in 2014 showed very strong plumes coming from the top of the seamount. The plumes had high turbidity, low pH, strong anomalies in reduced chemicals, and very high levels of hydrogen (figure 5).

Figure 5. Cross-section over the top of Daikoku seamount measured on 14 December 2014 with the results from a CTD tow (black line), showing turbidity anomalies (warm colors indicate high particle concentrations) in the plume. Courtesy of 'Submarine Ring of Fire 2014 – Ironman' expedition, NOAA/PMEL, NSF.

The 2014 bathymetry data revealed two summit craters; the larger one measured 150 m across and 100 m deep on the N side of the summit with a crater floor depth of 452 m below sea level, and the smaller one, about 50 m across on the NE flank, had a crater floor depth of 443 m below sea level. The bathymetry data from 2003 show only one small crater on the N side of the summit about 50 m across with a floor depth of 400 m below sea level (figure 6). The larger pit appeared to be about 70 m wider in 2014 than in 2006.

Figure 6. Bathymetric comparison of data collected at the Daikoku summit during the 2014 expedition (top) and in 2003 (bottom). The summit crater was significantly larger, and confirmed to be hydrothermally active by the CTD tow and midwater data collected by the 2014 expedition. A second crater has also appeared on the NE flank of the volcano. Arrows with numbers represent the depth below sea level (Z) in meters. Courtesy of 'Submarine Ring of Fire 2014 – Ironman' expedition, NSF/NOAA.

On 3 and 4 December 2016, the Schmidt Ocean Institute Research Vessel R/V Falkor travelled to the Mariana back-arc with a multidisciplinary team of scientists to gather evidence of active hydrothermal vents and the life they support. They were able to make two ROV (Remotely Operated Vehicle) dives at Daikoku and collected data on the seamount and sea life living there. On their first dive they observed (and sampled) a fissure with a sulfur chimney caked with yellow sulfur, emitting white bubbles and particulates in 70°C water (figure 7).

Figure 7. An active sulfur chimney at Daikoku on 3 December 2016 was videoed and sampled by the Schmidt Ocean Institute expedition. Upper Image: A fissure at Daikoku on 3 December 2016 with a yellow sulfur-caked chimney emitting white bubbles and particulates in 70°C water. Lower Image: The sulfur chimney was sampled by the ROV SuBastian for chemical analysis. Courtesy of Schmidt Ocean Institute, Expedition FK161129.

On their second dive on 4 December 2016, they collected tube worms and crabs, and recorded the formation of "sulfur needles," tadpole-shaped fragments of sulfur that were previously observed in sampled sediments and seen floating in the water column. They appear to form when gas bubbles (probably CO₂) rise through molten sulfur, forming a coating of sulfur around the bubble before the gas escapes (figure 8). Their video shows a sulfur chimney caked with yellow sulfur emitting yellow, white, and orange droplets of sulfur.

Figure 8. Tadpole shaped "sulfur needles" coat the side of a sulfur chimney at Daikoku on 4 December 2016 as gas bubbles coated with sulfur rise through the chimney and drip residue around the sides. A video recording was also made of the chimney emitting bubbles (https://schmidtocean.org/cruise-log-post/daikoku-dive-2-sulfur-good/). Courtesy of Schmidt Ocean Institute, Expedition FK161129.

The cruise scientists used the ship's EM302/710 multibeam echosounder to get a 2-m-resolution image of the summit crater, which they combined with water column data to create an image showing both the bathymetry of the volcano and the shape of the hydrothermal plume emitting from the summit (figure 9).

Figure 9. Multibeam echosounder data reveals the topography of the summit at Daikoku on 4 December 2016 as well as the shape of the hydrothermal plume emitting from the summit. Courtesy of Schmidt Ocean Institute, Expedition FK161129.

Geologic Background. The conical summit of Daikoku seamount lies along an elongated E-W-trending ridge SE of Eifuku submarine volcano and rises to within 323 m of the sea surface. It is one of about a dozen displaying hydrothermal activity in the southern part of the Izu-Marianas chain. A steep-walled, 50-m-wide cylindrical crater on the north flank, about 75 m below the summit, is at least 135 m deep and was observed to emit cloudy hydrothermal fluid. During a NOAA expedition in 2006, scientists observed a convecting, black pool of liquid sulfur with a partly solidified, undulating sulfur crust at a depth of 420 m below the summit. Gases, particulate with the appearance of smoke, and liquid sulfur were bubbling up from the back edge of the sulfur pool.

Information Contacts: Office of Ocean Exploration and Research, National Oceanic and Atmospheric Administration (NOAA), 1315 East-West Highway, Silver Spring, MD 20910, USA (URL: http://oceanexplorer.noaa.gov/, Cruise logs at: http://oceanexplorer.noaa.gov/explorations/03fire/logs/summary/summary.html, http://oceanexplorer.noaa.gov/explorations/04fire/logs/april15/april15.html, http://oceanexplorer.noaa.gov/explorations/06fire/logs/may4/may4.html, http://oceanexplorer.noaa.gov/explorations/14fire/logs/december14/december14.html); Schmidt Ocean Institute, 555 Bryant Street #374, Palo Alto, CA 94301, USA (URL: https://schmidtocean.org/, https://schmidtocean.org/cruise/searching-life-mariana-back-arc/.

Klyuchevskoy has been quite active for many decades, with eruptive periods alternating with less active times (BGVN 35:06, 38:07, and 39:10). Recent eruptions took place during August-December 2013, with another period of activity beginning in January 2015 and continuing at least into March 2015 (BGVN 39:10). MODVOLC thermal alert pixels, based on MODIS satellite data, were frequent starting on 3 January but had stopped after 26 February 2015. Moderate activity continued until 10 May 2015, when the eruption that began in January ended. Eruptive activity was again observed in late August 2015, and fluctuating activity has continued through March 2017. The Kamchatkan Volcanic Eruption Response Team (KVERT) is responsible for monitoring this volcano, and is the primary source of information. Times are in UTC (local time is UTC + 12 hours).

Activity during April-July 2015. KVERT lowered the Aviation Color Code (ACC) to Green, the lowest of four levels, on 6 April 2015, although moderate gas-and-steam activity continued. On 13 April, gas-and-steam emissions increased at 0840, and continued at least through 1215 on 14 April, with incandescence at the summit possibly indicative of renewed Strombolian activity. KVERT raised the ACC from Green to Yellow. Strong gas-and-steam activity continued through the rest of April; the plumes sometimes contained small amounts of ash. Satellite data showed a weak thermal anomaly when not obscured by clouds, and incandescence at the summit was occasionally observed. On 18 April, KVERT reported that Strombolian activity was continuing, and that a webcam had recorded a narrow ash plume rising 1-2 km and drifting 100 km SE; the ACC was raised to Orange. Satellite images showed a weak thermal anomaly during 16-17 and 23 April; a gas plume containing a small amount of ash drifted 147 km E on 21 April. On 26 April the ACC was lowered to Yellow; KVERT noted that gas-and-steam activity and tremor continued.

Satellite data showed ash-bearing plumes during 2-5 May that drifted more than 450 km SE, and moderate activity continued through 9 May. The ACC was briefly raised to Orange before again being set at Yellow on 12 May. Moderate activity prevailed though the rest of the month. Satellite data showed occasional gas-and-steam plumes, sometimes containing small amounts of ash; weak thermal anomalies were often observed over the volcano when clouds did not obscure viewing.

On 22 May, KVERT described activity as weak. This remained the case through 27 August 2015. Gas-and-steam emissions continued, and satellite data often showed a thermal anomaly when the volcano was not obscured by clouds. Gas-steam plumes drifted 20 km SE on 26-27 May. On 20 July, the ACC was lowered to Green.

Activity during August 2015-March 2016. On 27 August, KVERT reported that a moderate Strombolian explosion had occurred, which continued into 28 August. At 1544 UTC on 27 August, incandescence of the crater was observed. The ACC was raised to Yellow.

Thereafter, through 17 September 2015, KVERT described activity as moderate, with moderate gas-steam activity. Strombolian explosions occurred on 27-28 August and 8-10 September. Satellite data showed occasional weak thermal anomalies when the volcano was not obscured by clouds. On 13-14 September, a diffuse ash plume rose to about 1.5 km and drifted E.

During 24 September-30 November 2015, KVERT described the activity as a "weak explosive eruption." According to video data, moderate gas-and-steam activity continued and a weak thermal anomaly was sometimes observed when the volcano was not obscured by clouds. Occasionally, incandescence of the summit volcanic crater was noted.

KVERT again described activity as moderate during December 2015-March 2016, with strong gas-steam emissions, although the volcano was usually either quiet or obscured by clouds. KVERT reported thermal anomalies each month, ranging from two during December 2015 to 12 during both January and February 2016. Video often recorded incandescence at the summit during the latter part of December.

Activity during April 2016-November 2016. On 3 April 2016, activity increased with Strombolian explosions. Detection of very frequent thermal anomalies by the MODVOLC system began again on 8 April and continued being reported almost daily through 2 November 2016. Thermal data identified by the MIROVA system showed strong anomalies over the same time period (figure 18). The MIROVA data also indicated a steady increase in radiative power beginning in the second half of May 2016.

Figure 18. Plots of MODIS thermal data detected at Klyuchevskoi during the year ending on 23 March 2017. The data analyzed by the MIROVA system is presented as radiative power (top) and log radiative power (bottom). Courtesy of MIROVA.

Strong gas-steam emissions continued, and plumes extended to about 100 km SE on 10 April and about 55 km NE on 14-15 April. Satellite data by KVERT through June showed persistent intense thermal anomalies when not obscured by clouds. On 24 April, activity increased again. According to video and satellite data, a lava flow began to effuse on the S and SE flank of the volcano (along Apakhonchich chute). An ash plume drifted about 500 km SW on 23-24 April. The ACC was raised to Orange.

The explosive-effusive eruption continued from May through September 2016. Lava continued to effuse along the SE flank. Satellite data showed an ash plume extending 88 km SE on 2 May, up to 80 km E and SE on 13 May and 16 May, 47 km W on 13 June, about 30 km E on 18 June, and 60 km W and E on 27-28 June. Gas-steam plumes drifted about 60 km W and E on 27 and 28 June. On 24 June, at 2115 and 2350 UTC, video data showed two rock collapses into the Apakhonchich chute and ash plumes drifted W, then NW. According to video and satellite data, Strombolian activity of the summit crater continued on 24 June.

According to video data, the eruption intensified on 6 July. Strong explosions sent ash to an altitude of 7.5 km and the plumes drifted about 350 km SW, S, and SE. A large bright thermal anomaly was observed all that week. On 6-7 July, dense ash plumes drifted about 400 km SE and E, and numerous ash plumes were observed thereafter through September. Bursts of volcanic bombs shot up to 200-300 m above the summit crater and up to 50 m above the cinder cone into the Apakhonchich chute along the SE flank. Lava continued to flow on the SE flank along the chute (figure 19). Strong gas-steam activity within two volcanic centers emitted various amounts of ash. On 10, 13 and 15 September, explosions shot ash up to an altitude of 7 km and ash plumes extended for about 50 km SE and NE. The eruption with lava streaming down the Apakhonchich chute on

Figure 19. Photo of Klyuchevskoy on 25 August 2016 with ash-containing emissions and lava streaming from the cone into the Apakhonchich chute. Courtesy of Denis Bud'kov/Bernard Duick.

During the second week of September, KVERT reported that lava began to effuse on the E and SW flanks. Explosions sent ash up to an altitude of 7.5 km and ash plumes extended for about 530 km in various directions. Small ash layers were observed over Koryaksky and Avachinsky volcanoes on 8 September. On 10, 13, 15, and 20-22 September, explosions sent ash up to an altitude of 6-7 km and ash plumes extended for up to 165 km in various directions. In their 29 September and 6 October reports, KVERT noted that bursts of volcanic ash that rose above the summit crater and cinder cone fell into Apakhonchich chute.

Explosions during the first week of October sent ash to an altitude of 5-6 km and plumes extended about 260 km E. On 7-8 October, gas-steam plumes containing ash drifted about 390 km E and SE. By 13 October, activity had apparently diminished, with moderate gas-steam emissions containing some ash. A weak thermal anomaly was noted on 7 and 12 October.

By 20 October the explosive-effusive activity had returned with a lava flow on the E flank, a large strong thermal anomaly, and strong gas-steam emissions containing various amounts of ash. Explosions sent ash to 5-6 km altitude and plumes extended for about 300 km E, SE, and NW on 14 and 18-19 October. On 20-21 and 23-27 October explosions sent ash up to an altitude of 5-7 km; gas-steam plumes containing ash extended for about 335 km in various directions. On 30-31 October and 1-3 November, explosions sent ash up to an altitude of 5-8 km and gas-steam plumes containing ash extended for about 277 km E and SE. Strong thermal anomalies detected from satellite by the MODIS instrument decreased significantly in strength after 2 November.

On 3-5 November, ash plumes extended up to 116 km E. KVERT's report on 10 November noted that activity had decreased significantly during the previous week. Lava effusion onto the flanks was last noted on 3 November; the next day the thermal anomaly was weaker. Ash plumes were last detected in satellite images during 3-4 November. The ACC was lowered to Yellow on 7 November. However, moderate activity continued and thermal anomalies and Strombolian activity could still be observed. Strong gas-and-steam emissions continued. On 16 November, an ash plume extended up to 85 km NW. KVERT reported a daily thermal anomaly visible in satellite images during 18-25 November.

Activity during December 2016-March 2017. Thermal anomaly data after early November 2016 was not sufficient to cause alerts on MODVOLC, and was seen to be very weak and fluctuating in MIROVA plots before ending completely in mid-February 2017 (see figure 19). On 26 December KVERT reported that a weak thermal anomaly had been detected and that gas-and-steam plumes sometimes contained small amounts of ash. Over the next few months the ACC was frequently changed between Yellwo and Orange, depending on the ash plume hazard to aviation.

Explosions on 1 January 2017 generated ash plumes that rose to an altitude of 5 km and drifted 114 km SE, resulting in KVERT raising the ACC to Orange. Daily satellite imagery showed a thermal anomaly over the volcano during 2-6 January. Gas-and-steam emissions sometimes with minor ash, along with thermal anomalies, continued through 20 January. During 9-10 January ash plumes drifted 160 km ESE, and on 22 January an ash plume rose to 5-5.5 km and drifted 45 km E.

KVERT reported that a thermal anomaly was identified in satellite data during 25 February and 1-3, 5, and 8-9 March. At 1340 on 2 March a gas, steam, and ash plume recorded by the webcam rose to altitudes of 8-9 km and drifted 110 km NE and NW. Explosions on 8 March produced ash plumes that rose to 5.5 km altitude and drifted about 20 km NW. As of 24 March gas-and-steam emissions continued to rise from the crater, and a weak thermal anomaly was sometimes identified in satellite images, but no explosions had been detected since 8 March. On 24 March the ACC was lowered to Green.

A gas, steam, and ash plume identified in satellite data on 28 March rose to altitudes of 5-6 km and drifted 108 km ENE, resulting in the ACC being raised to Yellow. Another ash plume the next day that rose to as high as 7.5 km altitude and drifted 75 km SW prompted an Orange ACC status. Additional explosions during 27-30 March generated ash plumes to an altitude of 7 km that drifted 300 km in multiple directions.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (Email: kvert@kscnet.ru, URL: http://www.kscnet.ru/ivs/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Mount Rokatenda, or Paluweh, on the island of Palu'e, lies north of the primary volcanic arc that cuts across Flores Island in Indonesia's Lesser Sunda Islands, and has seen infrequent activity in modern times. The previous eruption in 1985 from a summit lava dome spread 3 cm of ash over villages on the W side of the island. This report is a summary of the October 2012 to August 2013 eruption, and an update through 2016 that includes information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and the University of Hawai'i's MODVOLC thermal alert reporting system. Numerous news reports also covered the major explosions during 2013.

Two brief periods of increased seismicity in April 2009 and January 2012 were the only recorded activity at Paluweh since 1985, prior to an eruption that began in October 2012 and continued through August 2013. PVMBG noted the beginning of lava dome growth on 8 October. A substantial number of MODVOLC thermal alert pixels from MODIS satellite data were first recorded on 11 October 2012 and recurred regularly through 20 July 2013. The first ash plumes were reported by the Darwin VAAC on 11 November 2012 and continued several times each month through May 2013, and then again in late June and during 10-12 August. Plumes generally rose to 2-3 km and drifted between 50 and 100 km in various directions, although a large ash plume on 3 February 2013 rose to higher than 13 km and drifted over 500 km SE, S and SW, briefly impacting air travel in NW Australia. A major explosion on 10 August 2013 created a large pyroclastic flow to the NW from the summit that killed five people on the beach. No further explosions were specifically dated after 12 August 2013, and seismicity gradually decreased over the next several months.

Activity during October 2012-April 2013. PVMBG noted lava dome growth, incandescent avalanches, pyroclastic flows, and ash plumes during October 2012 through January 2013. Ejecta as large as 6 cm in diameter was deposited up to 3 km from the summit, and ashfall affected the entire island, averaging 2 cm thick in places; lahars and ash damaged homes and infrastructure on the island (BGVN 39:01). A large eruption on 2 February 2013, which produced a 13-km-high ash plume the next day, generated a substantial SO2 signature, pyroclastic flows to the S and SW, and avalanches. Residents of eight villages were evacuated and significant ashfall was reported up to 1 mm thick in Ende (60 km S on East Nusa Tenggara Island). Thick ashfall was also reported in Ona (SE part of the island) and thin deposits were reported in other areas of the island to the W, N, and E. During a field expedition on 7 February, PVMBG staff observed that about 25% of the S portion of the dome was lost; the lava-dome volume had been an estimated 5.1 million cubic meters on 13 January, prior to the explosion.

After the large early February 2013 explosion, many intermittent low-level ash emissions continued through the last week in May, with over 175 VAAC reports issued from the Darwin VAAC during the period. NASA's Earth Observatory (EO) identified an ash plume in MODIS satellite images drifting over 440 km SW on 24 March 2013, and discoloration of the seawater from ash W of the island (figure 7).

Figure 7. NASA image acquired 24 March 2013 with the MODIS instrument shows an ash plume from Paluweh drifting over 440 km SW across Flores Island. Light-colored ash coats the southern third of Paluweh Island, and the ocean to the W of the island is colored turquoise from ash floating near the water's surface. Image posted at http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=80737. Courtesy of NASA, GSFC.

Another NASA-EO image captured on 19 April 2013 shows the extent of ash deposits covering areas of the S and E sides of the summit where the plumes most commonly drift. A delta extending S into the Flores Sea, which was visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion (figure 8), was also visible.

Figure 8. NASA-EO image of Paluweh captured 19 April 2013. Note the extent of ash covering the area of the island on the S and E sides of the summit where the plumes usually drift. It also shows a delta extending S into the Flores Sea, also visible in imagery on 12 February (http://earthobservatory.nasa.gov/IOTD/view.php?id=80422 ) and likely created by a pyroclastic flow during the large 2-3 February explosion. Courtesy of NASA Earth Observatory (ihttp://earthobservatory.nasa.gov/NaturalHazards/view.php?id=80987).

Activity during May-August 2013. There was a three-week break in reported ash plumes between 25 May and 19 June when a low level plume rising to 2.4 km was observed drifting 37 km SE. After this, no further activity was reported until 10 August. A large and deadly explosion took place on 10 August, producing an ash plume that rose to 4.3 km and drifted 130 km W. Details of the explosion are given in BGVN 39:01 and additional information is provided in this report. According to PVMBG, a substantial pyroclastic flow traveled NW from the summit down the Ojaubi drainage towards a village on the beach and killed five fisherman. Rescuers noted that the ground was hot and covered with 10-20 cm of ash. NASA-EO captured images before and after the 10 August 2013 eruption where the path of the pyroclastic flow to the NW is clearly visible (figure 9).

Figure 9. NASA-EO images of Paluweh (Mt. Rokatenda) on 3 August and 4 September 2013, before and after a large eruption with a deadly pyroclastic flow that travelled NW from the summit to the ocean, killing 5 people at the beach on 10 August. The delta on the S of the island was created during an earlier eruption and pyroclastic flow on 2-3 February 2013. Courtesy of NASA Earth Observatory ( http://earthobservatory.nasa.gov/IOTD/view.php?id=81986).

Activity during 2014-2016. In April 2014, PVMBG noted that the last major explosion had been on 10 August 2013. The last 2013 ash plume recorded by the Darwin VAAC was on 12 August 2013. Visual observations of occasional eruptive activity were noted until November 2013; small explosion earthquakes were also reported as being last recorded in November. No changes were observed in the lava dome between September 2013 and March 2014. PVMBG lowered the Alert level from III to II (on a scale of 1-4) on 7 April 2014.

No additional reports of activity at Paluweh appeared until late 2015, when PVMBG noted that steam plumes rising 75-200 m above the summit were common between August and October 2015. Seismicity remained low but variable during this time as well. From November 2015 through January 2016, steam plume heights ranged from 5-150 m. Seismicity remained low; earthquakes indicating rock avalanches and fumarolic emissions were the most common type recorded (figure 10). Paluweh remained quiet throughout 2016, although in February 2017 it was still listed by PVMBG at Alert Level II, with a potential for eruptive activity.

Figure 10. Seismic activity at Paluweh between 1 January 2015 and 13 January 2016. Vertical Axis represents daily number of events for all graphs. Guguran are avalanche events, Hembusan are emission-related events, Vulkanik Dangkal (VB) are shallow volcanic events, Vulkanik Dalam (VA) are deep volcanic events, Tektonik Local are local tectonic events, and Tektonik Jauh are distant tectonic events. Courtesy of PVMBG (Paluweh report, 18 January 2016).

Geologic Background. Paluweh volcano, also known as Rokatenda, forms the 8-km-wide island of Palu'e north of the volcanic arc that cuts across Flores Island. The broad irregular summit region contains overlapping craters up to 900 m wide and several lava domes. Several flank vents occur along a NW-trending fissure. The largest historical eruption occurred in 1928, when strong explosive activity was accompanied by landslide-induced tsunamis and lava dome emplacement. Pyroclastic flows in August 2013 resulted in fatalities.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

A brief eruption that began on 23 October 2013 was the first reported activity at Zhupanovsky since 1959 (BGVN 39:09). After another eight months of quiet, eruptive activity began again in early June 2014 that was characterized by periods of frequent, moderate, ash-generating explosions that continued through the end of that year (BGVN 39:09). As described below, similar activity continued from January 2015 through 24 March 2016, with periods of strong explosions generating ash plumes as high as 10 km altitude. Another long period of eight months without observed activity was broken by a large eruption on 20 November 2016. No additional activity was reported through March 2017. Most of the data comes from Kamchatka Volcanic Eruption Response Team (KVERT) reports. Often, the volcano is obscured by clouds. All reported dates are UTC unless otherwise noted (local = -12 hours).

Activity during 2015. According to KVERT, the moderate eruption with explosions generating ash plumes continued into 2015 (table 1). The Aviation Color Code remained Orange (third level on a four-color scale) between 1 January and 15 May 2015. After an explosion on 3 April, explosive activity waned and KVERT lowered the Aviation Color Code from Orange to Yellow (second level on a four-color scale) on 16 May. On 9 June 2015, activity increased again, with webcam and satellite images showing an ash plume rising to an altitude of 6 km. The Aviation Color Code was raised on 8 June to Orange.

During an overflight on 16 July, volcanologists observed fresh deposits at the foot of the volcano from collapses of the S section of the active Priemysh Crater that likely occurred on 12 July (figures 7 and 8). Moderate activity at the crater continued through 17 July; the Aviation Color Code was lowered to Yellow on 18 June and to Green on 23 July.

Figure 7. Photo of the summit area of Zhupanovsky showing the collapse deposits from the Priemysh cone, 16 July 2015. Photo credit to A. Plechova and V.I. Vernadsky, IGAC RAS. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 8. Photo of the southern side of Zhupanovsky showing the collapse deposits from the Priemysh cone, 16 July 2015. Photo credit to A. Plechova and V.I. Vernadsky, IGAC RAS. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

On 7 August KVERT reported that explosive activity had ended, but collapses of the S part of the active crater continued. On 6 August ash plumes rose to an altitude of 5 km and drifted 25-60 km SW, triggering KVERT to raise the Aviation Color Code to Yellow. The code was lowered back to Green on 13 August.

KVERT indicated that activity remained low until 27 November 2015 when, based on satellite images, ash plumes rose to altitudes of 5-6 km and drifted 285 km E. The Aviation Color Code was raised to Orange. IVS FED RAS (Institute Volcanology and Seismology Far East Division of the Russian Academy of Sciences) observers noted an ash explosion at 0356 on 30 November (UTC); the Tokyo Volcanic Ash Advisory Center (VAAC) reported that the resulting ash plume rose to an altitude of 9 km. Pyroclastic flow deposits 15.5 km long were observed on the S flank after the 30 November event.

According to KVERT, activity decreased after a partial collapse of the S central sector on 27 and 30 November 2015. Satellite images detected a very weak thermal anomaly over the volcano on 4 and 7 December. Moderate levels of fumarolic activity continued. On 10 December the Aviation Color Code was lowered to Yellow. By early-to-mid December 2015, only moderate levels of fumarolic activity were observed. On 17 December the Aviation Color Code was lowered to Green.

KVERT reported that thermal anomalies occurred frequently during the reporting period; often they were obscured by clouds. The only MODVOLC thermal alerts, based on MODIS anomalies, during the reporting period were during March-June 2015: on 7 March, 8 March (2 pixels), 15 March (2 pixels), 21 March (2 pixels), 20 May, and 16 June.

Table 1. Summary of reported activity at Zhupanosky, January 2015-March 2016. Data is from webcam images, satellite images, and visual observations. On many days, clouds obscured visibility. Courtesy of KVERT and Tokyo VAAC.

Activity during 2016. The eruption pattern of fluctuating activity levels continued into 2016. Based on visual observations, KVERT reported that at 1636 on 19 January 2016 (UTC), an explosion generated an ash plume that rose to an altitude of 7-8 km and drifted 20 km E (figure 9). The Aviation Color Code was raised to Orange.

Figure 9. Photo of the ash column rising from Zhupanovsky, 19 January 2016. Still image taken from webcam video. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Moderate steam-and-gas activity continued during 5 February-18 March. An explosion at 2029 on 12 February (UTC) was recorded by a video camera and generated an ash plume that rose to an altitude of 7 km and drifted E. A larger explosion visually observed a minute later generated an ash plume that rose to an altitude of 10 km and drifted 50 km SE. The Aviation Color Code was raised to Red for several hours. In a report issued at 2334 (UTC), KVERT noted that only moderate amounts of gas and steam rose from the volcano; the Aviation Color Code was lowered to Orange. Ash from the earlier explosions drifted E over Kronotsky Bay and NW. A few hours later, an ash plume was detected in satellite images rising 1 km above the volcano and drifting 288 km E.

The Tokyo VAAC recorded an explosion at 1320 on 24 March (UTC) that generated an ash plume which rose to an altitude of 8 km. After the explosion, no further activity was observed. A very weak thermal anomaly was detected over the volcano in satellite images on 1 and 10 April. The Aviation Color Code was thus lowered to Yellow on 13 April. The last thermal anomaly detection in a satellite image was on 10 April. However, moderate fumarolic activity continued. The Aviation Color Code was lowered to Green on 16 June.

At 1429 on 20 November 2016 a webcam recorded ash plumes rising to altitudes of 6-8 km and drifting 73 km E (figure 10); the Aviation Color Code was raised from Green to Orange. No further activity was observed, and on 22 November the Aviation Color Code was lowered to Yellow.

Figure 10. Photo of the ash column rising from Zhupanovsky and extending E, 20 November 2016. Still image taken from webcam video. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Geologic Background. The Zhupanovsky volcanic massif consists of four overlapping stratovolcanoes along a WNW-trending ridge. The elongated volcanic complex was constructed within a Pliocene-early Pleistocene caldera whose rim is exposed only on the eastern side. Three of the stratovolcanoes were built during the Pleistocene, the fourth is Holocene in age and was the source of all of Zhupanovsky's historical eruptions. An early Holocene stage of frequent moderate and weak eruptions from 7000 to 5000 years before present (BP) was succeeded by a period of infrequent larger eruptions that produced pyroclastic flows. The last major eruption took place about 800-900 years BP. Historical eruptions have consisted of relatively minor explosions from the third cone.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences, (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).