Activity for the week of 21 July-27 July 2004
The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 2300 UTC every Wednesday, notices of volcanic activity posted on these pages are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.
New Activity / Unrest
| Flores Island (Indonesia)
| 8.676°S, 122.455°E
| Elevation 1661 m
According to DVGHM, an eruption began at Egon on 25 July at 2240, consisting of loud rumbling sounds, a strong sulfur scent, and explosions that rose to 1-1.5 km above the summit. A thick, black plume drifted NNW from the volcano. Interpretations of seismic data revealed that the eruption lasted about 2.5 hours. According to the Darwin VAAC, a plume was visible on satellite imagery. DVGHM reported that about 630 residents near Egon self evacuated from the villages of Egon, Nangatobong, and Itoper. According to a news article, about 1,400 people evacuated. At 1500 on 26 July seismographs recorded nearly continuous explosions produced plumes to ~250 m above the volcano.
Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC), Agence France-Presse (AFP)
| 1.22°N, 77.37°W
| Elevation 4276 m
Based on information from IG, the Washington VAAC reported that an activity increase at Galeras during several days prior to 24 July consisted of emissions that rose ~600 m above the volcano's summit. Ash was not visible on satellite imagery. According to a news report, a wide area around the volcano was declared off limits to visitors.
Sources: Washington Volcanic Ash Advisory Center (VAAC), Associated Press
| Lomblen Island (Indonesia)
| 8.272°S, 123.505°E
| Elevation 1423 m
A pilot reported that a thin plume emitted from Lewotolo was at a height of ~300 m above the summit on 25 July. Ash was not visible on satellite imagery.
Source: Darwin Volcanic Ash Advisory Centre (VAAC)
| United States
| 61.299°N, 152.251°W
| Elevation 3374 m
AVO raised the Concern Color Code at Spurr from Green to Yellow on 26 July after an increase in seismicity was recorded beneath the volcano's summit. Some earthquakes were interpreted to reflect the beginning stages of volcanic unrest. AVO noted that there were no indications that an eruption was imminent and that this type of seismicity can decline without leading to an eruption.
Retrospective analysis suggested that the seismic increase began slowly, perhaps as early as February 2004. As of 26 July, the seismic network recorded 15-20 earthquakes daily. This rate was greater than any observed since the last eruptive period in 1992. All earthquakes were less than magnitude 1.5 and ranged in depth between 1 and 6 km below sea level. Relatively few earthquakes were located beneath the Crater Peak vent, the site of the 1953 and 1992 eruptions. On 11 July a pilot reported a strong sulfur smell from Spurr and a new area of steaming, but AVO scientists observed neither during an overflight on 15 July.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
| Mariana Islands (USA)
| 16.35°N, 145.67°E
| Elevation 790 m
Seismicity at Anatahan approached the highest levels of the year on 23 July. That day, Strombolian explosions frequently threw mostly coarse material up to hundreds of meters at intervals of tens of seconds to minutes. On 26 July, there were nearly continuous ash-and-gas emissions. By 27 July, seismicity had decreased to very low levels in comparison to the previous 2 months, and seismic signals indicated that the frequent individual explosions that occurred during the previous week decreased greatly in size and number.
Sources: Emergency Management Office of the Commonwealth of the Mariana Islands and United States Geological Survey Volcano Hazards Program, Hello Pacific News
| 14.473°N, 90.88°W
| Elevation 3763 m
A series of strong explosions at Fuego on 21 July during 0630-0950 produced ash plumes to a height of ~2 km above the volcano. Plumes traveled W, SW, and S, depositing ash in several villages near the volcano. Small incandescent avalanches of volcanic material traveled to the mouths of several ravines. Ash emissions and avalanches continued through 27 July.
Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)
| Hawaiian Islands (USA)
| 19.421°N, 155.287°W
| Elevation 1222 m
Several surface lava flows were visible at Kilauea during 22-26 July, and all vents in the crater of Pu`u `O`o were incandescent. Seismicity was weak beneath Kilauea's summit and tremor at Pu`u `O`o was at moderate-to-high levels. During 22-25 July, deflation occurred at Pu`u `O`o.
Source: US Geological Survey Hawaiian Volcano Observatory (HVO)
| Luzon (Philippines)
| 13.257°N, 123.685°E
| Elevation 2462 m
According to a news article, during the week of 18 July emissions from Mayon deposited ash on two villages near the volcano. Reportedly, a PHIVOLCS scientist stated that the explosions may have occurred due to water contacting hot rocks.
Source: Associated Press
| DR Congo
| 1.52°S, 29.25°E
| Elevation 3470 m
According to the Toulouse VAAC, an eruption began at Nyiragongo sometime before 0700 on 27 July. Satellite imagery showed that the plume produced from the eruption rose to between 3.6 and 4.9 km a.s.l.
Source: Toulouse Volcanic Ash Advisory Centre (VAAC)
| 14.757°N, 91.552°W
| Elevation 3745 m
During 21-27 July, weak-to-moderate explosions from Santa María's Santiaguito lava-dome complex produced plumes to heights ~700 m above the volcano. During the report period, several avalanches of volcanic material traveled SW down Caliente cone.
Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC)
| 16.72°N, 62.18°W
| Elevation 915 m
Volcanic and seismic activity at Soufrière Hills remained at low levels during 16-23 July. The seismic network recorded seven hybrid earthquakes and seven rockfalls. No long-period events or volcano-tectonic earthquakes were recorded. The sulfur-dioxide flux on 16 and 23 July was 170 and 400 metric tons per day, respectively.
Source: Montserrat Volcano Observatory (MVO)
| 1.467°S, 78.442°W
| Elevation 5023 m
During 25-26 July, volcanic and seismic activity were at low levels at Tungurahua. A few sporadic long-period earthquakes were related to small emissions from the volcano. Inclement weather prohibited observations of the emissions.
Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG), Washington Volcanic Ash Advisory Center (VAAC)
| United States
| 56.17°N, 159.38°W
| Elevation 2507 m
Small steam-and-ash emissions were accompanied by periods of volcanic tremor at Veniaminof during 16-23 July. On 22 July at 1229, an AVO field crew witnessed a small ash burst rise a few hundred meters above the summit of the intracaldera cone. This type of activity prevailed at Veniaminof during the previous 3 months. During periods of repose in the report week, the cone produced variable amounts of white steam from at least two separate craters near its top. The snow-and-ice field over much of the caldera was covered with a discontinuous, 1- to 2-mm thick ash blanket. Veniaminof remained at Concern Color Code Yellow.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
Criteria & Disclaimers
The Weekly Volcanic Activity Report does not necessarily include all volcanic activity that occurred on Earth during the week. More than a dozen volcanoes globally have displayed more-or-less continuous eruptive activity for decades or longer, and such routine activity is typically not reported here. Moreover, Earth's sea-floor volcanism is seldom reported even though in theory it represents the single most prolific source of erupted material. The Weekly Volcanic Activity Report summarizes volcanic activity that meets one or more of the following criteria:
- A volcano observatory raises or lowers the alert level at the volcano.
- A volcanic ash advisory has been released by a volcanic ash advisory center (VAAC) stating that an ash cloud has been produced from the volcano.
- A verifiable news report of new activity or a change in activity at the volcano has been issued.
- Observers have reported a significant change in volcanic activity. Such activity can include, but is not restricted to, pyroclastic flows, lahars, lava flows, dome collapse, or increased unrest.
Volcanoes are included in the "New Activity/Unrest" section of the Weekly Volcanic Activity Report if the activity occurs after at least 3 months of quiescence. Once a volcano is included in the "New Activity/Unrest" section, updates will remain in that section unless the activity continues for more than 1 month without escalating, after which time updates will be listed in the "Continuing Activity" section. Volcanoes are also included in the "New Activity/Unrest" section if the volcano is undergoing a period of relatively high unrest, or increasing unrest. This is commonly equal to Alert Level Orange on a scale of Green, Yellow, Orange, Red, where Red is the highest alert. Or alert level 3 on a scale of 1-4 or 1-5.
It is important to note that volcanic activity meeting one or more of these criteria may occur during the week, but may not be included in the Weekly Volcanic Activity Report because we did not receive a report.
1. The Weekly Volcanic Activity Report is intended to provide timely information about global volcanism on a weekly basis. Consequently, the report is generated rapidly by summarizing volcanic reports from various sources, with little time for fact checking. The accuracy of the Weekly Volcanic Activity Report is dependent upon the quality of the volcanic activity reports we receive. Reports published in the Bulletin of the Global Volcanism Network are monthly, and more carefully reviewed, although all of the volcanoes discussed in the Weekly Volcanic Activity Report are not necessarily reported in the Bulletin. Because of our emphasis on rapid reporting on the web we have avoided diacritical marks. Reports are updated on the Weekly Volcanic Activity Report web page as they are received, therefore information may be included regarding events that occurred before the current report period.
2. Rapidly developing events lead to coverage that is often fragmentary. Volcanoes, their eruptions, and their plumes and associated atmospheric effects are complex phenomena that may require months to years of data analysis in order to create a comprehensive summary and interpretation of events.
3. Preliminary accounts sometimes contain exaggerations and "false alarms," and accordingly, this report may include some events ultimately found to be erroneous or misleading.
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