AVO reported that on 2 August the Volcano Alert Level for Cleveland was raised to Watch and the Aviation Color Code was raised to Orange due to the formation of a 40-m-wide lava dome in the summit crater that was observed on 29 July. The lava dome was extruded sometime after 7 July following the last clear view of the summit area, however thermal anomalies observed since 19 July suggested that the dome had extruded since that time.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

Sezione di Catania - Osservatorio Etneo reported that in the evening of 28 July Strombolian explosions from the active vent on the E flank of Etna's SE Crater cone were weak and sporadic, then ceased during the night. Throughout 29 July the crater was quiet. In the early morning of 30 July intermittent incandescence from the crater gradually intensified and became more frequent, then was followed by intense Strombolian activity accompanied by loud detonations. Lava bombs ejected several tens of meters fell back into the crater or around the rim. A diffuse ash plume drifted E. A small lava flow on the E flank descended about 100 m then rapidly chilled. The activity was accompanied by a distinct increase in the mean amplitude of volcanic tremor that, along with the activity, abruptly decreased in the early afternoon.

Later that day the mean amplitude of volcanic tremor increased again along with Strombolian activity. A diffuse gas-and-ash plume again drifted E. Strombolian activity intensified and incandescent jets became continuous. At the same time lava flowed E and the effusion rate rapidly increased; lava flowed 3 km down the W slope of the Valle del Bove. The ash plume became more dense and ashfall was reported in the Ionian area (18 km E). During the most intense period, fragments of fluid lava were ejected 450-500 m above the crater and fell onto the flanks of the pyroclastic cone to distances of 200-300 m. Lava fountains jetted from at least two vents located within the crater and on the upper E flank, roughly aligned WNW and ESE. The activity ceased just after midnight. The event on 30 July was the eighth paroxysmal event in 2011.

Source: Sezione di Catania - Osservatorio Etneo (INGV)

CVGHM reported increased seismicity from Marapi during 21 June-3 August. Observers noted that during June and July white plumes rose 15-75 m above the summit craters. On 1 August white plumes rose 15 m above the main crater; fog prevented observations the next day. On 3 August dense gray plumes rose 300-1,000 m above the crater on eight occasions. That same day CVGHM raised the Alert Level to 2 (on a scale of 1-4). Visitors and residents were prohibited from going within a 3-km radius of the summit.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

OVSICORI-UNA reported that on 23 July a group of observatory scientists visited Poás to document changes that had occurred there during the previous weeks. They noted that the subtle, semicircular scarp observed a few months earlier had rapidly progressed to a sharp scarp on the SE shore of Laguna Caliente. The 60-m-wide, 2.5-m-high scarp degassed and geyser activity was observed on the W end, next to the steaming lake. In an area about 40 m above the surface of the lake where there were fractured rocks and vigorous gas venting, incandescence emanated from the lava dome and a temperature of 670 degrees Celsius was measured.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)

RVO reported that white vapor occasionally tinted blue rose from Rabaul caldera's Tavurvur cone during 1-28 July. Dull incandescence emanated from a small caved-in vent on the floor of the crater. The start of an ash eruption on 29 July was marked by an emergent low-frequency tremor and slowly rising gray ash plumes. One explosion on 30 July possibly produced light ashfall to the NW. Seismic data indicated forceful degassing on 1 August.

Source: Rabaul Volcano Observatory (RVO)

Sezione di Catania - Osservatorio Etneo reported that during the late evening of 1 August a vast accumulation of incandescent material appeared at the base of Stromboli's N1 vent, the northernmost active vent within the crater terrace at about 750 m elevation. Within a few minutes, the material collapsed and slid downslope, creating two small lobes of lava. The more easterly flow descended the N slope of the Sciara del Fuoco, generating small landslides from the loose material on the slope, and marking the first lava effusion event outside of the crater since a small emission during 11-12 December 2010. The lava accumulated on a flat area near hornitos that were formed during 2002-2003, before continuing further down a steep slope. On 2 August the lava had descended to 500 m elevation and advanced very slowly. During the afternoon effusion appeared to have diminished.

Source: Sezione di Catania - Osservatorio Etneo (INGV)

Based on information from JMA, the Tokyo VAAC reported that during 27 July-2 August plumes from Sakura-jima rose to altitudes of 1.8-3 km (6,000-10,000 ft) a.s.l. During 28-30 July and 1 August, pilots observed ash plumes that rose to altitudes of 2.1-3 km (7,000-10,000 ft) a.s.l. Plumes occasionally drifted SW, S, SE, and W.

Source: Tokyo Volcanic Ash Advisory Center (VAAC)

KVERT reported that during 22-29 July moderate seismic activity continued at Karymsky and possible ash plumes rose from the crater. A thermal anomaly on the volcano was detected by satellite during 22 and 24-27 July; cloud cover prevented observations on the other days. The Aviation Color Code remained at Orange.

Based on information from Yelizovo Airport (UHPP), the Tokyo VAAC reported that on 30 July an ash plume rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted SW.

Sources: Kamchatkan Volcanic Eruption Response Team (KVERT), Tokyo Volcanic Ash Advisory Center (VAAC)

HVO reported that two lava lakes at Kīlauea were active during 27 July-2 August. The level of the summit lava lake fluctuated deep in the 150-m-diameter vent inset within the E wall of Halemaʻumaʻu Crater and circulated with various patterns. Periodic measurements indicated that the gas plume from the vent continued to deposit variable amounts of ash and occasionally fresh spatter nearby.

Lava from the Puka Nui and MLK pits, smaller craters to the W of the main Puʻu ʻŌʻō crater, continued to overflow to the SW, producing a tube-fed pāhoehoe flow that had advanced about 700 m from the Puka Nui rim during 25-30 July. Lava from the base of the NE crater filled a trough between the crater wall and the perched lava lake. Uplift of the crater floor and lava lake continued until 30 July, when a breakout lava flow started along the base of the crater's S wall and the lake slowly subsided. Subsidence continued the next day but switched to inflation on 1 August. The preliminary sulfur dioxide emission rate from all east rift zone sources was calculated at 1,700, 1,000, and 800 tonnes/day on 29 and 30 July, and 1 August, respectively.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

KVERT reported that photos taken of Kizimen on 20 July showed that the lava flow on the E flank, which began in January, remained active. During 22-29 July seismicity was above background levels and weak volcanic tremor continued to be detected. Satellite images showed a bright thermal anomaly on the volcano all week and seismic data indicated that possible ash plumes rose to an altitude of 3 km (10,000 ft) a.s.l. Seismologists in the area observed the active lava flow on the E flank. The Aviation Color Code remained at Orange.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

During 25 July-1 August, OVDAS-SERNAGEOMIN reported that the eruption from the Cordón Caulle rift zone, part of the Puyehue-Cordón Caulle volcanic complex, continued and seismicity indicated that the lava flow remained active. Cloud cover prevented observations by a video camera on 25 July, though satellite imagery detected a plume that drifted 200 km SE. On 26 July the camera recorded a plume that rose 2 km above the crater and incandescence up to 500 m above the crater was observed at night. Satellite imagery showed a plume drifting 100 km SE. Cloud cover again prevented camera observations during 27-28 July, but on 28 July a 150-km-long plume was observed in satellite imagery drifting SE. During 29-31 July plumes rose 2-5 km above the crater and satellite imagery showed plumes drifting 80-400 km SW, N, and NE. Incandescence was observed up to 300 m above the crater at night during 29-30 July. Cloud cover prevented observations on 1 August. The Alert Level remained at Red.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)

KVERT reported that seismic activity at Shiveluch was moderate during 22-29 July and indicated that possible ash plumes rose to an altitude of 4.7 km (15,400 ft) a.s.l. during 23 and 25-27 July. Satellite imagery showed a thermal anomaly on the lava dome on 22 July; cloud cover prevented observations on other days. Ground-based observers noted fumarolic activity on 24 July. The Aviation Color Code remained at Orange.

Based on information from KEMSD, the Tokyo VAAC reported that on 1 August an eruption produced a plume that rose to an altitude of 7 km (23,000 ft) a.s.l. and drifted E. Ash was seen in subsequent satellite images that same day.

Sources: Kamchatkan Volcanic Eruption Response Team (KVERT), Tokyo Volcanic Ash Advisory Center (VAAC)