Event Name : Great Sitkin phreatic 2018
|Start:||June 10, 2018 ||Observed|
|Stop:||December 11, 2018 ||Observed|
|Fumarolic or hydrothermal activity: ||
Earthquake activity at Great Sitkin increased in early June, 2018. At 11:39 AKDT (19:39 UTC), June 10, a signal that may represent a short-lived steam explosion was detected by seismic data. In response, AVO raised the Aviation Color Code and Volcanic Alert Level from GREEN/Normal to YELLOW/Advisory. Oblique airphotos and satellite images taken after the explosion showed a small (about 2 km) ash deposit, extending southwest from the vent. This deposit was likely the result of the explosion on June 10, 2018.
On June 27, citing declining seismicity and no further indication of unrest, AVO lowered the aviation color code and volcanic alert level to GREEN/Normal.
On July 1, earthquake activity increased above background levels and AVO located numerous small, shallow earthquakes occurring beneath the summit at rates as high as 10-20 per hour. In response, AVO raised the color code and alert level to YELLOW/Advisory.
Low-level unrest continued, and another small phreatic explosion signal was observed in seismic data at 11:05 am AKDT on August 11, 2018. Small local earthquakes preceded the event and stopped after the phreatic explosion. This event was similar to the June 10, 2018 event.
Low-level unrest continued, and a a minor tremor burst was recorded on Tuesday, September 18, 2018. A small explosion was detected seismically on November 5, though it was not seen in regional infrasound data and no ash cloud was observed in satellite data, and others on Novermber 16 and December 11.
Earthquake activity decreased in February, 2019, and AVO lowered the aviation color code and volcanic alert level to GREEN/Normal on February 25, 2019.