The April 11, 2022, earthquake “swarm” was located under the Mt. Edgecumbe crater, which itself is part of a larger volcanic field called the “Southwest Rift.” These geological features all stem from the Queen Charlotte Fault, the boundary between the North American and Pacific plates located just 12 km offshore. (Alaska Earthquake Center image)

UPDATE April 23, 2022:

Satellite radar data from the Alaska Volcano Observatory indicates that there has been steady uplift since 2018 in a large area to the east of the Mt. Edgecumbe crater, “consistent with an intrusion of new material (magma) at about 5 km (3.1 miles) below sea level.” (AVO image)

The Alaska Volcano Observatory on Friday (4-22-22) released new information which appears to confirm that the recent earthquake “swarm” under Mt. Edgecumbe (4-11-22) is the result of volcanic activity, rather than the background tectonic activity of the Queen Charlotte Fault.

An analysis of satellite radar data over the last year shows significant uplift over an 11-square mile area just east of the Mt. Edgecumbe crater — totaling almost 11 inches. The deformation has been occurring at a steady rate of over 3 inches per year since 2018, and “there has not been an increase with the recent earthquake activity.”

The AVO offers this prognosis on the situation at Mt. Edgecumbe:

The coincidence of earthquakes and ground deformation in time and location suggests that these signals are likely due to the movement of magma beneath Mount Edgecumbe, as opposed to tectonic activity. Initial modeling of the deformation signal shows that it is consistent with an intrusion of new material (magma) at about 5 km (3.1 miles) below sea level. The earthquakes likely are caused by stresses in the crust due to this intrusion and the substantial uplift that it is causing.

Intrusions of new magma under volcanoes do not always result in volcanic eruptions. The deformation and earthquake activity at Edgecumbe may cease with no eruption occurring. If the magma rises closer to the surface, this would lead to changes in the deformation pattern and an increase in earthquake activity. Therefore, it is very likely that if an eruption were to occur it would be preceded by additional signals that would allow advance warning.

ORIGINAL REPORT April 20, 2022:

An expert on marine geology and a leading researcher on the Queen Charlotte Fault believes the recent earthquake “swarm” under Mt. Edgecumbe near Sitka is consistent with volcanic activity.

Dr. Gary Greene is not suggesting an eruption is imminent – if one occurs at all – but he does think signs are pointing to the upward movement of magma below Mt. Edgecumbe, which has been dormant for centuries.

The Queen Charlotte Fault runs offshore Southeast Alaska, almost perfectly straight, for over 500 miles.

It’s a rare geological feature – called a “leaky transform fault” – where the North American and Pacific plates continually slip past each other.

Because it’s a plate boundary, the Queen Charlotte Fault is deep, extending down through the Earth’s crust and into the mantle. Thousands of years ago, the movement of the fault opened a conduit in the crust, and molten magma pushed through and formed the Mt. Edgecumbe volcano.

Dr. Gary Greene thinks that the April 11 earthquake swarm indicates that the process may be underway again.

“When magma starts heading towards the surface it re-melts the rock that is there and it fractures that rock and the fracturing is what causes the earthquake,” said Greene. “So as the magma starts to move up into the crust and and gets closer to the surface, you start getting these, these low magnitude earthquakes, which were experienced last week (April 11). And then it can shut off, which it sounds like it has now. But it can start again any time and if the fault moves some more, it can cause dilation again and then cause more magma to start reaching up towards the surface.”

Greene is retired from a long career with the US Geological Survey. He’s an emeritus professor at the Moss Landing Marine Lab at San Jose State University, and he holds a research faculty position with the University of Washington’s Friday Harbor Lab.

But his specialty of late has been mapping the undersea Queen Charlotte Fault, and the Mt. Edgecumbe volcano is a product of that fault. The Queen Charlotte is tectonically active, and reliably produces measurable earthquakes – which usually propagate laterally along the fault.

The April 11 “swarm” was located under the mountain, and the quakes appeared to migrate upward from deep in the crust to shallower depths. But like his peers at the Alaska Volcano Observatory, Greene says it’s too early for dire predictions.

“The good sign is that this might just be a hiccup,” said Greene. “It just started and there wasn’t much pressure below, or much dilation, to cause this thing to really start to break towards the surface in an explosive event, but it also could be a precursor to what may occur sometime in the future.”

Mount St. Helens, as seen during its eruption in May 1980. The stratovolcanoes of the Cascades were produced as the result of plate subduction. Located along a “leaky transform fault” (or plate boundary), a Mt. Edgecumbe eruption — if it occurs — would be far less dramatic, and more along the lines of the Hawaiian volcanoes, according to Greene. (USGS image)

Most Sitkans by now are probably envisioning Mt. Edgecumbe blowing its top, and clouds of ash billowing into the sky like the famous eruption of Mount St. Helens in 1980. Again, Greene says the structure of the Queen Charlotte Fault probably wouldn’t lead to anything that dramatic. He pictures something a bit more tame.

“This volcano is not like the volcanoes that sit down off of Seattle, for instance. And it’s not like a St. Helens volcano. So these types of volcanoes generally have a small amount of explosive activity at the beginning of an eruption. A lot of ash will come out. But generally after a while it dies down and they’re more similar to a Hawaiian type of volcano.”

One of the most active volcanoes in Hawaii isn’t on the big island itself, but just offshore. Greene says this could be a possibility for Mt. Edgecumbe, which isn’t a lone volcanic peak, but one crater of many in a large volcanic field along the “Southwest Rift” which links Kruzof Island – where Mt. Edgecumbe is located – to the Queen Charlotte Fault 12 kilometers away, under the sea floor. An eruption somewhere on the rift is as much a possibility as an eruption on Mt. Edgecumbe – no one knows for sure right now. Although he’s mainly a student of the fault, Greene is glad the USGS is taking an active interest in what’s happening at Mt. Edgecumbe. “If I were really studying the volcano in any detail,” he says, “I’d want to get some instruments out there.”