Increased seismic activity under Trident volcano, Alaska

trident october 12 2022

On February 22, 2023, the Alaska Volcano Observatory (AVO) raised the alert level of Trident Volcano to ADVISORY and the Aviation Color Code to YELLOW due to an increase in seismic activity beneath the volcano. The last eruption at this volcano was in 1974 (VEI 3).

Earthquakes under Trident are occurring at an average rate of about 10 per day since January 1, 2023. The earthquake depths are mostly located in the shallow crust, with depths less than 6 km (3.7 miles) below sea level.

This activity began on August 24, 2022, with depths mostly around 25 km (15.5 miles) below sea level, and became progressively shallower to around 5 km (3.1 miles) over the following four days. The largest event since August was an M4.6 quake on November 20, but most earthquakes are much smaller.

The recent increase in seismic activity does not indicate an imminent eruption of Trident, and AVO has not detected any other signs of unrest.

trident volcano seismicity 2003 - 2023
Earthquakes located beneath Trident Volcano, Alaska, from January 1, 2003, to February 21, 2023. The bar graph shows the number of earthquakes recorded per month. A swarm of relatively deep earthquakes started on August 24, 2022, and shallow earthquake activity remains elevated through February 2023. Credit: USGS/AVO, Aaron Wech

Increases in seismic activity have been detected previously at Trident and other similar volcanoes, with no subsequent eruptions. The Alaska Volcano Observatory expects additional shallow seismicity and other signs of unrest, such as gas emissions, elevated surface temperatures, and surface deformation to precede any future eruption if one were to occur.

Trident Volcano’s eruptive history includes multiple explosive eruptions, with a maximum Volcanic Explosivity Index (VEI) of 3. The most recent confirmed eruption occurred on July 15, 1974, with a maximum VEI of 3. Other confirmed eruptions with a maximum VEI of 3 occurred in 1968, 1967, 1964, 1963, 1962, and 1953. An eruption with a maximum VEI of 2 occurred in 1961, 1957, and 1950. An eruption with a maximum VEI of 1 occurred in 1913 (September).

Geological summary

The Trident stratovolcano cluster was named for the three prominent peaks that were the most visible features at the summit prior to 1953.

The andesitic-dacitic group consists of four overlapping stratovolcanoes and numerous flank lava domes, including Falling Mountain and Mt. Cerberus on the far west flank.

The summit complex is located 3 – 5 km (1.8 – 3.1 miles) SE of Novarupta volcano, and merges along a ridge to the NE with Katmai.

The three oldest Trident volcanoes are glaciated and Pleistocene in age, while the youngest, Southwest Trident, was formed during historical time.

Eruptions migrated through time from the NE to the SW. In 1953 a new lava dome began growing on the SW flank of Trident I volcano.

A series of thick andesitic lava flows were erupted between 1953 and 1968, forming a cone with 400 – 800 m (1 312 – 2 624 feet) of local relief.

Periodic explosions took place until 1974, and the current summit contains a 350 m (1 148 feet) wide crater.

Some of the distal lava flows from West Trident stratovolcano collapsed into the Novarupta vent during its 1912 eruption.2


1 Trident volcano – AVO/USGS Volcanic Activity Notice – Issued on February 22, 2023

2 Trident volcano – Geological summary – GVP

Featured image credit: USGS/AVO, Matt Loewen


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