Why are there so many volcanoes in the Pacific Northwest and Alaska?

 
The distribution of volcanoes in the northwest and Alaska is the result of plate tectonics. In the northwest, the oceanic Farallon Plate is being pushed beneath (subducted) the continental margin of the North American Plate. When the subducted plate comes in contact with the hot asthenosphere beneath the continental plate conditions are right for the [...]

Redoubt, Alaska, USA

On 18 March, AVO lowered the Alert Level for Redoubt to Advisory and Aviation Color Code to Yellow because seismicity declined to levels recorded prior to the ash emission on 15 March. Seismicity remained low the next day. Shallow earthquake activity was noted again on 20 March. On 21 March, a steam plume rose to [...]

Koryaksky, Kamchatka Peninsula, Russia

KVERT reported that seismic activity at Koryaksky was elevated on 13 March and at background levels on the other days during 14-20 March. Observers reported that gas plumes containing a small amount of ash rose to an altitude of 4 km (13,200 ft) a.s.l. and drifted in easterly directions during the reporting period. The plumes [...]

Hunga Ha’apai, Tonga

Based on information from Tonga Meteorological Services, analysis of satellite imagery, and pilot observations, the Wellington VAAC reported that during 18-19 March ash plumes from Hunga Tonga-Hunga Ha’apai rose to altitudes of 4-5.2 km (13,000-17,000 ft) a.s.l. and drifted NE and about 480 km ENE. On 20 March, steam plumes rose to an altitude of [...]

Galeras, Colombia

On 24 March, INGEOMINAS lowered the Alert Level for Galeras to III (Yellow; “changes in the behavior of volcanic activity”). During the previous week daily sulfur dioxide levels were high. Earthquake levels were low in both intensity and occurrence. During 21-23 March, white-colored gas plumes rose to an altitude of 5.4 km (17,700 ft) a.s.l. [...]

Amazing Tongan Eruption Photos

Alan Taylor from the Big Picture Blog on Boston.com has posted some amazing images of the Tongan eruption. I’d link there directly except the public comments are just not exactly… well… scientific.
Here are a few low rez linked out versions while they last though!

 
 

How do volcanoes affect the atmosphere and climate?

This photo shows the large white billowing eruption plume from Rabaul being carried in a westerly direction by the weak prevailing winds. At the base of the eruption column is a layer of yellow-brown ash being distributed by lower level winds. A sharp boundary moving outward from the center of the eruption in the lower [...]

Ash from Redoubt

After two months of restlessness and a day of heightened earthquake activity, Alaska’s Mount Redoubt Volcano erupted explosively on Sunday, March 22, 2009, at 10:38 p.m. Alaska Daylight Time, according to the Alaska Volcano Observatory. Overnight, four additional large eruptions occurred, the fifth one larger than the previous ones. Scientists estimated the plume reached a [...]

Semeru, Eastern Java, Indonesia

Based on information from CVGHM, the Darwin VAAC reported that on 12 March an eruption from Semeru produced a plume to an altitude of 4.6 km (15,000 ft) a.s.l. Ash was not identified on satellite imagery.
Sources: Darwin Volcanic Ash Advisory Centre (VAAC) – “Reports provided courtesy of the Smithsonian’s Global Volcanism Program and the US [...]

Redoubt, Alaska, USA

AVO reported that during 11-15 March seismic activity at Redoubt was low but remained above background levels. On 12, 14, and 15 March clear web camera views showed steam plumes that rose just above the summit. At about 1305 on 15 March, seismic activity increased and about four hours of volcanic tremor ensued. AVO scientists [...]