Seismic unrest continues at Spurr volcano in Alaska with over 900 earthquakes detected in 2024
Seismic activity at Mount Spurr volcano in Alaska remains elevated, with over 900 earthquakes detected so far in 2024, according to the Alaska Volcano Observatory (AVO). Despite the persistent unrest, no major shifts in earthquake frequency or intensity have been observed since the increase in seismic activity was first noted in April.
A small lake formed in the summit crater of Mount Spurr in early summer 2024 from melting ice. The lake has grown slightly over the summer, but no other changes in the lake or the nearby steam vents have been observed. Image credit: AVO
Elevated seismic activity first detected at Mount Spurr in April has been continuing at a rate of around 20 earthquakes per week.
As of October 9, the Alaska Volcano Observatory (AVO) had detected over 900 earthquakes this year, with the largest being an M2.3 on Sunday, October 6.
The earthquakes have been clustered in two areas: one at a depth of up to 10 km (6 miles) beneath the volcano, and the other roughly 20 – 35 km (12 – 22 miles) southeast of the crater peak vent.
No significant changes in the frequency or size of the quakes have been observed since April when the elevated activity was first detected.
Ground deformation near the flanks of the volcano began in March and has been consistent with the ongoing inflation of the volcano, as measured by Global Navigation Satellite System (GNSS) stations on site. The AVO has recorded approximately 4 cm (1.6 inches) of horizontal movement since March.
“The current increase in earthquake activity has some similarities to past episodes of increased seismic activity at Mount Spurr, including August 1991 to June 1992, which preceded the 1992 eruptions, and 2004 to 2006, when increased seismic activity accompanied heating at the summit that melted a substantial portion of the ice cap,” the AVO reported.
Preliminary modeling suggests that pressurization due to magma or fluid inflow, or gas exsolution, is occurring at a depth of 3 – 5 km (1.8 – 3 miles) and about 3 – 4 km (1.8 – 2.4 miles) west of Mount Spurr. Satellite radar data spanning September 2023 to September 2024 confirmed the GNSS-detected deformation around the volcano.
A small lake formed over the summit crater of Mount Spurr early in the summer, first appearing between May 15 and June 15. During an overflight of the area on June 23, the lake was roughly the size of a football field. It grew slightly over the summer, reaching a diameter of 85 m (280 feet) and an area of 0.5 ha (1.4 acres) due to minor collapses and melting of glacial ice inside the crater.
According to the latest updates, the lake is partially covered by ice and remains blue-green. Active steaming from summit-area fumaroles is visible along and above the northeastern lake shore and crater wall, as well as from a pit in the ice on the northeast crater rim. No visible changes in the intensity of steaming have been observed.
No volcanic mudflows or other signs of significant ice and snow melt have been observed in the summit region or at Crater Peak.
The last time a crater lake formed at the summit of Mount Spurr was during seismic unrest and a likely magma intrusion in 2004, which did not lead to an eruption.
The current Volcano Alert Level is Normal and the Aviation Color Code is Green.
The last eruptive phase of Mount Spurr occurred at the Crater Peak from June 27 to September 17, 1992, with a Volcanic Explosivity Index estimated at 4.
The last known eruption from the summit of Mount Spurr was more than 5 000 years ago.
Mount Spurr, the closest volcano to Anchorage, is located about 130 km (80 miles) west of the city, just northeast of Chakachamna Lake. Its summit features a large lava dome situated at the center of an amphitheater approximately 5 km (3.1 miles) wide, open to the south. This amphitheater was shaped by a late-Pleistocene or early Holocene debris avalanche and pyroclastic flows that destroyed an older volcanic structure. The avalanche traveled over 25 km (15 miles) southeast, leaving deposits that include blocks as large as 100 m (328 feet) in diameter.
The youngest vent, Crater Peak, formed at the southern end of this amphitheater and has produced about 40 Holocene tephra layers. Eruptions from Crater Peak in 1953 and 1992 sent ashfall to Anchorage.
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.
1 ALASKA VOLCANO OBSERVATORY INFORMATION STATEMENT – USGS – Released at 21:21 UTC on October 9, 2024.
2 Geological summary for Spurr volcano – GVP – Accessed October 11, 2024
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