Description: From Cameron and others, 2023: "In 2018, Mount Okmok (a name which herein includes associated volcanic features outside Okmok Caldera, such as Jag Peak and Tulik Volcano) continued the long-term reinflation that began immediately after its last eruption in 2008. This deformation takes place in discrete pulses that appear modulated onto a lower-rate, steady background deformation pattern. In 2018, monitoring stations OKCE and OKNC recorded a complete pulse, with a total horizontal displacement of about 10 centimeters (cm) [4 in] and a vertical displacement of as much as 12 cm [4.7 in]. Past analyses of geodetic data (GPS and InSAR) indicate a shallow magma reservoir exists underneath the caldera floor (for example, see Freymueller and Kaufman, 2010; Lu and Dzurisin, 2014), and the continued volcanic inflation is consistent with an ongoing accumulation of shallow melt. Mount Okmok’s Aviation Color Code and Volcano Alert Level remained at GREEN and NORMAL throughout 2018."
From Orr and others, 2023: "In 2019, Mount Okmok continued the long-term reinflation that began after its last eruption in 2008. This deformation takes place in discrete pulses that appear modulated onto a lower-rate, steady background deformation (for example, Xue and others, 2020). Like in 2018, a complete pulse took place in 2019 and was visible in the time series of monitoring station OKCE. The total displacement values were much less for the 2019 pulse, however, producing amplitudes of 4-5 centimeters (cm) [1.6-2 inches] in the horizontal and ~5 cm [2 in] in the vertical components. These are roughly half the amplitudes of the horizontal and vertical components recorded in the 2018 pulse. Past analyses of geodetic data (GNSS and InSAR) suggested a magma reservoir lies 2-3 km [1.2-1.9 mi] below sea level beneath the caldera floor (for example, Freymueller and Kaufman, 2010; Lu and Dzurisin, 2014), but more recent work suggests the existence of a shallow sill at 0.9 km [0.6 mi] and a pressure point source at 3.2 km [2 mi] below sea level (Xue and others, 2020). Regardless, continued inflation of the volcano is consistent with ongoing accumulation of melt at shallow depths.
"AVO scientists identified several seismic tremor episodes at Mount Okmok in September 2019. These began with a short tremor burst recorded on September 4 following observations of a few deep, low-frequency earthquakes on August 21 and 24. Several more tremor bursts were recorded on September 5. A series of longer (2-3 minute) tremor bursts took place on September 6, with bursts recurring every 10 minutes for about 90 minutes. AVO observed similar seismic activity again on September 9. The tremor episodes were not formally locatable, but the difference in tremor amplitudes between seismic stations suggests the tremor took place near cone A. Note that cone A and the other cones in Okmok Caldera have no formal names; the names used herein are informal.
"In addition to monitoring this activity through daily seismic checks, AVO implemented internal seismic and infrasound alarms to detect any increases in unrest. Satellite data showed no signs of unrest at Mount Okmok during these events, and the local infrasound array recorded no acoustic emissions. A retrospective analysis, however, found that the tremor onset coincided with a stop in the long-term inflation signal typically seen in geodetic data. Intermittent tremor bursts continued after the early September activity before finally subsiding in late November. The tremor bursts of 2019 did not lead to greater unrest, so the Aviation Color Code and Volcano Alert Level of Mount Okmok remained at GREEN and NORMAL throughout the year."
From Orr and others, 2024: "In 2021, Mount Okmok continued the long-term deformation trend that began immediately after its 2008 eruption. This deformation takes place as discrete inflationary pulses superimposed onto a lower-rate, steady background inflation and is consistent with ongoing accumulation of melt at shallow levels. One such pulse was recorded in 2021, appearing on the time-series plots for GNSS stations OKCE, OKNC, and OKSO. The total displacements of the 2021 pulse were similar to the totals of 2019 but larger than those of 2020 (see, for instance, the OKCE time series in figure 31 [in the original reference]), with amplitudes of 4-5 cm [1.6-2 in] in the horizontal and ~5 cm [~2 in] in the vertical components. This inflation is roughly half that of 2018, when the volcano underwent ~10 cm [~4 in] of horizontal displacement and as many as 12 cm [4.7 in] of vertical displacement (Cameron and others, 2023).
"From roughly the beginning of October through November 2021, Mount Okmok departed from its common deformation pattern by producing an additional inflationary pulse, prompting AVO to release an Information Statement. This pulse, which was observed at stations OKCE and OKNC, was consistent with a pressure increase at less than 1 km [0.6 mi] depth that had a source located near Cone D, south of Ahmanilix. Past analyses of GNSS and InSAR geodetic data suggest a shallow magma reservoir exists underneath the caldera floor of Mount Okmok (for example, Freymueller and Kaufman, 2010; Lu and Dzurisin, 2014)."