Event Name : Iliamna 2013/2
|Start:||February 2, 2013 ||Observed|
|Debris-avalanche, volcanic avalanche, or landslide: ||
|Fumarolic or hydrothermal activity: ||
|Geomorphologic change without eruptive cause: ||
|Eruption Type:||Not an eruption.|
From Dixon and others (2015): "Activity at Iliamna Volcano in 2013 was highlighted by the observation of three significant rock/snow/ice avalanches, which often are seen on Iliamna. Monitoring highlights included a flight to measure gas emissions in April and substantial upgrades to AVO's geophysical monitoring network in August and September. Iliamna began 2013 at Aviation Color Code and Volcano Alert Level YELLOW/ADVISORY, based on seismicity interpreted to be caused by a magmatic intrusion (Neal and others, 2012). On January 9, 2013, citing decreasing seismicity, AVO downgraded the Aviation Color Code and Volcano Alert Level to GREEN/NORMAL, and Iliamna remained at this level throughout the rest of 2013.
"On February 2, 2013, seismic signals indicated that a substantial avalanche had occurred on the eastern flank of Iliamna on the Red Glacier (fig. 3 in original text) at 13:58 UTC (4:58 a.m. AKST). This slide was preceded by 3 days of elevated seismicity with more than 40 earthquakes, several as large as ML=3. An hour before the avalanche, small, repeating earthquakes occurred, gradually increasing in rate to merge into a continuous signal. After about 5 minutes of sustained broad-frequency signal, the sequence abruptly ended, signaling the end of the avalanche. This avalanche also produced a signal seen on the infrasound array at Dillingham, Alaska, approximately 320 km (200 mi) southwest of Iliamna. Poor weather obscured views of the volcano, and prevented immediate visual confirmation of the avalanche. AVO mentioned the avalanche in the February 8, 2013 weekly update, noting that avalanches are common at Iliamna, and are not indicative of volcanic unrest. Later in February, AVO received visual confirmation of the avalanches when a local resident sent photographs from early February, showing the avalanche deposits on the Red Glacier (fig. 4 in original text).
"On April 18, AVO scientists conducted a gas-measurement flight to Iliamna. During this flight, they detected emissions slightly greater than Iliamna's long-term background values (C. Werner, U.S. Geological Survey, written commun., 2013). Iliamna's typical fumaroles were visible and documented by AVO observers on the gas-measurement flight.
"On July 24, a citizen observer used the 'Is Ash Falling?' notification system on AVO's Web site to report 'increased' steaming without ash on Iliamna's eastern flank during the evenings of the week of July 15. AVO noted no anomalous seismicity or evidence of increased steaming in satellite data. When Iliamna is backlit in the evening hours, as viewed from the Kenai Peninsula, its normal fumarolic plume often appears more prominent.
"During August and September, AVO improved and upgraded geophysical equipment at Iliamna. Two new broadband seismometers were installed at pre-existing station sites ILW and IVE with a Web camera at site IVE.
"Satellite data from August 25 showed two modest avalanches down the northern-northeastern flank of Iliamna. On September 20, AVO received photographs of a new, significant, eastern flank avalanche at Iliamna (fig. 5 in original text). AVO had incomplete seismic data through September and AVO was not able to find evidence of the event in the existing seismic data. As determined in satellite imagery, the avalanche had a headwall scarp measuring 300 m (980 ft) wide by 40 m (130 ft) tall; source-to-terminus, the feature was about 1,200 m (3,940 ft) long.
"A photograph taken by a local resident on November 5 clearly depicts a flow feature on the eastern flank of Iliamna (fig. 6 in original text). A review of seismic records revealed a landslide at 16:32 UTC (7:32 AKST) on November 5. Careful analysis of seismic data on November 5 and 6 suggests two additional smaller avalanches after the larger one, although we do not have further photographic confirmation."