Pavlof Sister (left) and Pavlof (right) volcanoes, as viewed from the north (Bering Sea side).

Pavlof Sister (left) and Pavlof (right) volcanoes, as viewed from the north (Bering Sea side).

Date: Jul 17th, 2018
Volcano(es): Pavlof Pavlof Sister
Photographer: Mulliken, Katherine
URL: avo.alaska.edu/image/view/118291

Pavlof non-eruptive activity 2018

From Cameron and others, 2023: "The number of located earthquakes at Pavlof Volcano increased in 2018 compared to previous years. Although this increase was at least in part due to improvements to the local seismic network, there are indications that seismic activity in 2018 was nonetheless above background levels. Shallow LP earthquakes are common at the volcano, and the relative amplitudes of their waveforms, as observed by the Pavlof Volcano seismic network, indicate they tend to be located at or near the volcano summit. Although these events are commonly too small to be located by AVO’s routine earthquake location procedures, they are observable on spectrograms and are still noted in AVO’s routine seismic checks (Power and others, 2020). Similar activity has been observed at other open-vent systems in the Aleutian Arc, such as Shishaldin Volcano (Petersen and others, 2006; Pesicek and others 2018) and Mount Veniaminof (Pesicek and others, 2018), and appears to be typical for such systems (Quezada-Reyes and others, 2013).
"The Pavlof Volcano seismic network [in 2018] consists of three broadband digital seismic stations (PN7A, PS1A, and PS4A), three short-period 3-component stations (PV6A, PVV, and HAG), and one short-period vertical-component station (BLHA). The current configuration is fairly new; AVO carried out substantial upgrades to the network in the summer of 2017, during which PN7A, PS1A, PVV, and PS4A were upgraded to broadband digital stations, PV6 was replaced by PV6A, and HAG was upgraded from a vertical-component analog station to a 3-component station (Dixon and others, 2019).
"AVO located 152 earthquakes within a 20-kilometer radius of Pavlof Volcano in 2018...Throughout 2018, the volcano remained at Aviation Color Code GREEN and Volcano Alert Level NORMAL. Of the events that occurred in 2018, 111 were designated as LP earthquakes and 41 as volcano-tectonic (VT) earthquakes...Moderately deep LP earthquakes (10-20 km [6-12 mi] deep) took place in a broad swath east of Pavlof Volcano and Pavlof Sister throughout 2018, and although these events appear to be well-located based on reported root mean square errors (0.05-0.33), they often had small magnitudes.
"On March 27, 2018, an unusual cluster of VT earthquakes took place about 6-8 km [3.7-5 mi] north-northwest of Pavlof Sister and 12-13 km [7.5-8 mi] north of Pavlof Volcano. The earthquakes were 6.6-9.0 km [4.1-5.6 mi] below sea level with local magnitudes (ML) between 0.3 and 1.5. Later, in early April, a sequence of deep LP earthquakes took place near Pavlof Sister. These events were 10.1-29.3 km [6.3-18.2 mi] below sea level with ML values between −0.37 and 1.99, but only two events from the sequence were above ML 1.0. On September 11, another series of deep LP earthquakes took place in the same location as the March LP earthquake activity. The September 11 sequence had nine events, the two largest being ML 1.3 and 1.4. The hypocentral depths of these nine events ranged from 26 to 32 km [16-20 mi]. The sequence was also accompanied by a short tremor episode lasting about four minutes, though the tremor may have actually been closely spaced LP earthquakes.
"Volcano-tectonic earthquakes are not as common at Pavlof Volcano as at other volcanic systems, making the March 2018 brittle failure sequence notable. These events are assumed to have been distal VT earthquakes on the basis of their location (12-13 km [7.5-8 mi] from Pavlof Volcano), though they also may have been tectonically generated. AVO has not located any similar cluster in the same area since it began monitoring the volcano in 1996. The fact that there were more located events in 2018 than in previous years is not surprising given the network improvements made in 2017. Many of the 2018 events were of small magnitudes, and the increase in earthquake locations is partly due to the improved network. However, the additional presence of the March VT earthquake cluster and the LP earthquakes above ML 1.0 indicate the 2018 activity may have been above background levels for the upgraded network, suggesting increased magmatic activity at Pavlof Volcano in 2018. Alternatively, this behavior may be typical for the volcano but is only observed now because of the improved network.
"Observations made by Power and others (2004) of deep LP earthquake activity throughout the Aleutian Arc suggest a link between magma movement in the lower to middle crust and eruptive activity, although the timing between these parameters appears to vary. The deep LP earthquake activity at Pavlof Volcano may indicate the presence of continued magma supply to the volcano, with 2018 a slightly more active year. Further monitoring of earthquake activity at Pavlof Volcano will likely shed light on the magmatic system that feeds eruptive activity at the volcano."

Image courtesy of the AVO/ADGGS.
Please cite the photographer and the Alaska Volcano Observatory / Alaska Division of Geological & Geophysical Surveys when using this image.
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