Friday, June 29, 2012

Alaska's Mt Spurr Has Glacial Outburst Flood

Alaska's mt Spurr volcano, which last erupted in 1992, depositing ash on nearby Anchorage, AK, had a glacier outburst flood (or jökullhlaup if you like the Icelandic tongue twister) which lasted about 45 minutes after a period of weak, shallow quakes. This is pretty common in a lot of glacier-clad volcanoes, and especially in Iceland where geothermal activity routinely melts water under a glacier's surface, which results in a 'burst' of water escaping, causing sudden floods.

This does not mean the Spurr is gearing up for an eruption, as this could merely be normal behavior for the volcano (as also occurred in 1993, with no subsequent eruption), however this is one of the signs that volcanologists look for as a potential warning. If for example, the volcano began to do this rather regularly, there might be cause for concern. For now AVO has not raised the alert level, and probably will not unless the event repeats itself.

AVO's report is below:

61°17'56" N 152°15'14" W, Summit Elevation 11070 ft (3374 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN

Early on the morning of June 25 a minor increase in seismicity occurred at Mount Spurr. The character of the seismicity recorded was consistent with the seismic energy generated by an energetic flow of water, possibly a glacier outburst flood on the lower south flank of Mount Spurr. The flow was a single event lasting about 45 minutes and was associated with several discrete shallow earthquakes up to magnitude 1 in size. Within hours of the onset, seismic levels declined to near background and no additional flowage signals were observed. Visitors to the area were advised to use caution if in or around the drainages on the south flank of Mount Spurr, especially those draining Kidazgeni glacier, and the Chakachatna River east of Kidazgeni Creek. A similar flowage event occurred on June 29, 1993.

Mount Spurr volcano is an ice- and snow-covered stratovolcano located on the west side of Cook Inlet approximately 120 km (75 mi) west of Anchorage. The only known historical eruptions occurred in 1953 and 1992 from the Crater Peak flank vent located 3.5 km (2 mi) south of the summit of Mount Spurr.

These eruptions were brief, explosive, and produced columns of ash that rose up to 20 km (65,000 ft) above sea level and deposited several mm of ash in south-central Alaska, including approximately 6 mm of ash on Anchorage in 1953. The last known eruption from the summit of Mount Spurr was more than 5,000 years ago. Primary hazards during future eruptions include far-traveled ash clouds, ash fall, pyroclastic flows, and lahars or mudflows that could inundate drainages all sides of the volcano, but primarily on the south and east flanks."

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