Seward Peninsula Volcanic Fields

Mount Bendeleben, Alaska  http://www.summitpost.org/bendeleben-and-belt-lakes/805779

Earlier this year there was a significant earthquake swarm in Northwestern Alaska, north of the Seward Peninsula. While this wasn’t a swarm in the normal volcanic sense of a swarm (hundreds to thousands of smaller earthquakes in a period of hours to days), it was enough to get the attention of the locals who weren’t used to that level of activity. The largest quake was June 16, with a magnitude of 5.7, which is quite strong in that part of the state. http://www.aeic.alaska.edu/~shake/shake/11292524/intensity.html

Espenberg region, Alaska  http://www.earth-of-fire.com/article-alaska-la-peninsule-de-seward-les-maars-d-espenberg-117514124.html

So what does an amateur volcanaholic do when earthquakes start breaking out in the middle of nowhere? This one takes a look to see if that area had a history of volcanic activity. It turns out that a look there are at least three volcanic fields some 150 km south and east of the area of the earthquakes, which was a surprise. Some of the activity may have been within the last several thousand years.

Checked with the Alaska Volcano Observatory to see if there was any excitement afoot. They wrote back that the quakes were tectonic in nature; all connected to local fault lines that had decided to wake up over the spring and early summer. The faults are mostly buried and do not manifest themselves real well on the surface. The region is remote, with few people on the ground, and permafrost ranges to some 60 M below the surface. The AIEC database shows the region fairly active for the last 15 years or so. http://www.adn.com/article/20140615/earthquake-swarm-near-noatak-continues-puzzling-scientists

Approach into Buckland, Alaska  http://simple.wikipedia.org/wiki/Buckland,_Alaska#mediaviewer/File:Buckland_Alaska_aerial_view.jpg

But the notion that there were volcanic fields in the region, relatively recently active intrigued me so here is a bit of a science report on a part of the state I never visit.

Location

The volcanic fields are located some 150 – 200 km north and east of Nome, Alaska. Nome sits on the southern side of the Seward Peninsula in the far western part of the state. This is the part of the state closest to Siberia.

Nome is the destination of the largest sporting event in Alaska, our yearly dog race, the Iditarod, which celebrates the successful delivery of diphtheria serum from Anchorage to Nome by dogsled in 1925. The event was recreated as a race starting in 1967. The trail is around 1,800 km long and these days a winning team takes some 8 – 9 days to make the trip. The start is in Anchorage the last weekend in February, so temperatures are generally cold. http://en.wikipedia.org/wiki/Iditarod_Trail_Sled_Dog_Race

Nome was also the site of a couple gold rushes around the turn of the 20^th Century and went through the typical boom and bust cycles of the Western US during the 19^th Century. It is one of the largest cities in the region with a population of around 3,800.

Volcanics

Volcanic Fields on the Seward Peninsula  Image courtesy AVO/ADGGS, Janet Shaefer, http://www.avo.alaska.edu/images/image.php?id=50371

The three volcanic fields are the Espenberg, Imuruk Lake and Koyuk-Buckland Volcanic fields. They are part of the larger Bering Sea Volcanic Province, which has been sporadically active over the last 30 MY. The activity in the province can be traced back as far as 30 MY starting in the Koyuk – Buckland volcanic field. This is also the least well known volcanic field in the region, mostly due to its age and remoteness. Activity in the Bering Sea Volcanic Province picked up significantly some 6 MY ago beginning in the Imuruk volcanic field and continued More recent activity has been higher volume eruptions in and around the Bering Sea west and south of Nome. The majority of eruptive material is basalts.

There is more than a little head scratching about the source of magma for this region. It sits some 250 to over 1200 km to the north of the Aleutian Arc and the associated volcanic activity to be a standard back-arc volcanic province. Models tying the magma to rifting or mantle plume / hot spot powered volcanism have not been conclusively demonstrated either.  http://deepblue.lib.umich.edu/bitstream/handle/2027.42/95605/jgrb14956.pdf?sequence=1&isAllowed=y

As you travel east across Alaska at the same latitude from the three volcanic fields to Fairbanks, you traverse a region with geothermal energy potential. It is called the Central Alaskan Hot Springs Belt. There are several locations with hot springs that express surface activity. Major fault lines are mostly along an east–west axis, relieving energy delivered into the state via the collision with the Pacific Plate along the Denali Fault. The hot spring belt is not thought to be tied to volcanism in any meaningful way.

http://www.uaf.edu/files/rap/Kolker%20dissertation%202008.pdf

Earthquake and fault map of Alaska  http://www.aeic.alaska.edu/html_docs/images/earthquakes_in_alaska.jpg

The Koyuk – Buckland volcanics is by the far the largest of these fields. It is also the oldest. At least one researcher connects it to the Imuruk Lake volcanic field, though others do not. It sits some 720 km NW Anchorage and is composed primarily by basalt out of over 40 cinder cones and small shield volcanoes. Some of the basalt measures 150 m thick. http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Koyuk-Buckland%20volcanics

Map of Koyuk – Buckland Volcanic Field  https://www.avo.alaska.edu/images/image.php?id=2954

The Imuruk Lake volcanic field was active for some 850,000 years starting some 6 MY ago. It deposited some 110 km3 over an area of 2,000 km2 over that time. More recent activity has deposited another 300 km2 with the newest flow being some 1,655 years old. It appears to have the lowest rate of eruptive material of all the volcanic fields studied in the Bering Sea Volcanic Province. It is comprised primary of basalts out of some 75 cinder cones surrounded by lava flows. There are a few small shield volcanoes complete with subsidence calderas and heights in the 100 m range. http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Imuruk+Lake

Cinder cone and lava flow in Imuruk Lake Volcanic Field  http://volcano.oregonstate.edu/monogenetic-fields-0

Map of Imuruk Lake Volcanic Field  http://www.avo.alaska.edu/images/image.php?id=2939

The furthest west field is the Espenberg Volcanic Field which is marked by four of the largest maars known to exist. The reason for the large size is the interaction of magma with permafrost and water. To put the size of these maars in perspective, they are similar in diameter with calderas formed after the Katmai – Novarupta eruption in 1912, Crater Lake, Oregon and Kilauea.

Map of Maars of Espenberg Volcanic Field  http://www.earth-of-fire.com/article-alaska-la-peninsule-de-seward-les-maars-d-espenberg-117514124.html

In order to understand what happened, we first need to understand what happened with the onset of the most recent round of ice ages starting some 2 MY ago. Not only the onset lead to the formation of glaciers which at times have covered much of the North American continent, but also led to the formation of permafrost over large areas of Siberia, Alaska, Canada and Scandinavia. Interesting enough, most of central, western and northern Alaska did not have glacial coverage during the last glaciation. Instead, the state got permafrost, permanent today in the northern third of the state. Depths of the permafrost range from some 100 M in the vicinity of the volcanic fields in question to nearly 800 M in the Prudhoe Bay oil fields, making the extraction of shallow well oil difficult at best. The other thing about this part of the state is that the soil is very wet, with ice comprising over 40% of the permafrost.

Devil Mountain Maars  http://www.howitworksdaily.com/how-crater-lakes-form/

The newest is called Devil Mountain Lake and it measures some 8 km in diameter. It was dug via series of blasts which appear to have taken place as melted permafrost laden material slumped into the original explosive pit. There is evidence of pyroclastic flows during the eruptive sequence, making it more complex than the typical one-shot maar.

The paper referenced in the Additional Reading section on the Espenberg maars describe steep sides of these maars.  Depth is measured today at the deepest at around the 100 m, the depth  of the permafrost layer, though it appears that the craters were excavated to at least twice that depth into the older bedrock and sediment.  Additionally, it is also not uncommon for methane to accumulate under permafrost and the possibility exists that the explosions were also fueled by methane being torched off.
Older activity in the field includes at least five small shield volcanoes and basalt lava flows.  These date from 1.6 MY to more recent.  The maars all appear to have formed after the basalt activity, perhaps indicating when large quantities of permafrost were finally present for the upwelling magma to interact with.

Conclusions

One oddity on these three fields it the switch from rather run of the mill basalt cinder cone, small shield volcano activity to maars, as Espenberg is the only one of these fields known to have maars, though a pair of older lakes in the Imuruk Volcanic Field are suspected to also have maar-like activity.  The switch appears to be related entirely to the presence of permafrost brought about by the cyclic ice ages of the last 2 MY.

One final thought:  In these days of highly politicized climate science here in the US, it is getting increasingly difficult to find actual data on permafrost without wading through hundreds of recent articles on the warming, melting arctic and the horrors it will bring.  On a personal basis, I would rather my SciFi be labeled as such.

Imuruk Lake Volcanic Field  http://www.avo.alaska.edu/images/image.php?id=1973

– agimarc