When putting together a quick post on the most recent Pavlof eruption, I came across its home, the previously unknown (to me) Emmons Lake Volcanic Complex. Like the Katmai Volcanic Complex or the volcanic complex that contains Kamen, Tolbachik and Bezymianny in Kamchatka, Emmons Lake crams multiple active stratovolcanoes within a few tens of kilometers of one another. Like Katmai, this one also has a caldera, home of at least four major caldera eruptions over the last 350,000 years.
Emmons Lake Volcanic Complex is named after a crescent-shaped crater lake mostly filled by subsequent stratovolcanoes. It is located some 35 km E from King Cove, 45 km NE Cold Bay, and a mere 960 km SW from Anchorage AK. The surrounding communities are primarily fishing villages, supporting tourism in local National Wildlife Refuges, and providing Air Traffic Control support for civil aviation traffic on the Great Circle Route down the Aleutians. There are probably less than 2,000 permanent residents with a 50 km radius of the complex. Cold Bay is described as a regional transportation center.
The most significant feature in the area is multiple overlapping calderas, the largest of which measures some 9.5 x 17.5 km, one of the largest caldera complexes in the state. This caldera complex has tens of km3 of associated pyroclastic flows ejected during multiple eruptions.
There are at least three nested calderas in the western most portion of the complex formed during vigorous volcanic activity in the area over the last 400,000 years. There are a variety of intracaldera vents, cones, ash and lava flows in, breaching and extending outside the confines of the caldera walls. The farthest east portion of the caldera is punctuated by the cone of Little Pavlof volcano.
The “Gap” refers to a 9 km wide breach in the south wall of the caldera complex. It contains at least four “geologically significant silicic welded tuff units that have flowed through the gap within the last 234,000 years.”
Major stratovolcanoes associated with the complex include Mount Emmons, Mount Hauge, Double Crater, Little Pavlof, Pavlof and Pavlof Sister. Of these, the only cone that has no known historical eruptions is Mount Emmons. Everything is historically active, with Pavlof among the most active volcanoes in the entire state. These sit in a line on the order of 15 km long. https://www.hsdl.org/?view&did=26134
It appears that the complex was active well before the first caldera forming eruption some 400,000 years ago. Since then, there has been some 3 – 6 caldera forming eruptions. Estimated dates on these include 294,000, 234,000 123,000, 100,000, 30 – 50,000 and 26,000 years ago. Rhyolitic ash fall deposit from this eruption has been found some 1,700 km NE in the Klondike region of Canada. These were vigorous eruptions that produced highly mobile and very hot welded tuff. Some flows are found over 35 km from the source caldera. The most recent caldera forming eruption ejected pyroclastic flows that covered over 3,000 km3 and flowed up to 60 km from the caldera.
Two caldera forming eruptions were identified as the source of something called the Dawson tephra, 15 – 30 cm thick loess deposits, found in valley bottoms in the Yukon. One of these was some 238,000 years ago and the most recent one at some 26,000 years ago. Both were defined as ultra-Plinian events with plume heights in the 30 – 40 km range. Estimated output in each eruption is above 50 km3 with widespread ash dispersal. Both eruptions created currently observed caldera structures. The most recent eruption emplaced rhyolitic pumice flows covering a minimum area of 2,500 km2. Chemical analysis of the second eruption pyroclastics match very nicely the Dawson tephra found in the Yukon Territory, Canada. There is a question in the paper why a layer of the Dawson tephra has not been recognized elsewhere in Alaska. An answer might be that due to the vigorous volcanic, glacial and earthquake activity of Alaska between Emmons Lake and the Yukon, it might simply be drowned in the noise. http://cjes.geoscienceworld.org/content/40/7/925.full
In between caldera events, activity continues. There are multiple andesitic lava flows associated with two periods intra-caldera volcanic activity. We appear to be in the midst of the second episode of that activity. There are at least 20 lava flows associated with Mount Hague and nearby cinder cones. These lava flows are neither glaciated nor overgrown and are thought to be relatively recent.
Recent volcanic activity is mostly associated with Pavlof. Since 1790, it has had more than 40 reported eruptions, most less than the VEI 2 – 3 range, though these size eruptions have been reported. The majority of eruptions have otherwise been Strombolian in nature with some dust, bombs, cinders, blocky lava and lava fountains. The most vigorous Pavlof eruption observed was in 1911.
Mount Hauge has a vigorous fumarole field and a small crater lake well heated by fumarole activity. In the last 20 years, it has ejected small clouds of sulfur dioxide laden steam on multiple occasions that have been mistaken for explosions.
In a part of the world when heavy snowfall will grow glaciers, these volcanoes are remarkably unweathered, likely meaning that they regularly rebuild themselves. This also means that lahars are a continuing threat to the surrounding region.
Note that with the exception of Pavlof Sister, all of these volcanoes are closely spaced, sharing the same base in four cases, with the saddle between peaks and craters being a significant distance above the floor of the caldera.
Mount Emmons is the westernmost stratovolcano in the group. Its mass mostly displaces the crater lake partially filled with Emmons Lake. The volcano is some 1,325 m tall and has no historically observed activity. The volcano is primarily andesite with some low volume basaltic and low silica dacite lavas. The cone is glacially scoured and normally snow clad. http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Emmons%20Lake%20Volcanic%20Center
Mount Hague is the largest of the intracaldera volcanoes at some 1,540 m. The mountain is twin-peaked with a pair of craters, the southernmost filled with an acidic crater lake. The volcano also has a pair of vigorous fumarole fields, on located on the bottom of the crater lake that periodically braches and drains completely. The other is located on the southeast flank of Mount Hague. Steam plumes from this second fumarole field were reported as activity at least six times between 1990 – 2005. Like Mount Emmons, Hague is also snow and glacier clad year round. http://www.avo.alaska.edu/volcanoes/volcact.php?volcname=Emmons%20Lake%20Volcanic%20Center
Double Crater is the next volcano in line. With a height of some 1,360 m, it is topped with a nested pair of small craters. The entire mountain is also snow, ice and glacier covered year round. There has been no known historic activity. However, the craters look new, indicating relative recent activity. Like the first two volcanoes, Double Crater is primarily an andesite structure.
Little Pavlof Volcano punches through the eastern rim of the Emmons Lake caldera. It is some 2,040 m tall and covered with snow, ice and glaciers. As such, its past activity has been difficult to charachterize as has its composition, which is thought to be a combination of basalt and andesite. In photos, Little Pavlof looks like a satellite vent of Pavlof.
Pavlof is the tallest of this group of volcanoes at some 2,500 m. Like the others, it is snow, ice and glacier coveed. Unlike the others, it has been very active with over 40 eruptions observed since 1790. This makes it one of the most active volcanoes in the Aleutians, perhaps in the entire state. The majority of the eruptions are Strombolian in nature with limited fountaining, lava flows down the flanks. The majority of the eruptive products are andesitic and basalt. Many of the eruptions of Pavlof are larger, explosive in nature, well into the VEI 2 – 3 range. The largest eruption of Pavlof was a VEI 3 in 1911. Given that the volcano supports an extensive snow and ice cover, lahars are common during eruptive episodes and have clogged most of the drainages that head off the volcano. http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Pavlof
As of 25 Nov 2014, the eruptive episode that began on 12 Nov 2014 had been officially pronounced over.
Pavlof Sister is the farthest east volcano of the Emmons Lake Volcanic Complex. It is the only one that stands relatively alone. It is a single stratovolcano that tops out at some 2,140 m. Like the rest of the complex, it is mantled with snow, ice and glaciers. It is mostly andesite and basalt in construction with an extensive cover of tephra and pyroclastic deposits. There has been no observed activity on Pavlof Sister, though analysis of the deposits on its flanks indicate that it has operated much like Pavlof itself – mainly Strombolian type eruptions with occasional explosive blasts.
Finally, there are at least 12 large cinder cones present on the floor of the caldera complex. These are mostly scoria that is andesitic basalt in nature. The slopes and lava flows are steep and relatively fresh indicating they may be recent eruptions. Four of the cones have lava flows breaching the cones.
Given the relatively constant activity associated with Pavlof Volcano and the nearly complete filling of the last caldera with new stratovolcanoes, cones, vents, ash, lava and other eruptive products, I would suspect that the Emmons Lake Volcanic Complex is not finished with caldera-forming eruptions. It appears that the newer activity seems to be pushing a few kilometers east under Pavlof and Pavlof Sister. Watch this area closely, while it is not currently a very dangerous complex, given its history, things can get exciting in a very short time.