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Ice takes about two to three times more energy than liquid water to turn into steam, and that is part of why the lakes of the Espenberg Maars are so large. The National Park Service says the four Espenberg Maars, near the northern boundary of Bering Land Bridge National Preserve in Alaska, are the largest maar lakes in the world and the most northerly volcanic features in North America created during the Ice Age.
Aerial view of North and South Killeak Maar Lakes. NPS photo.
How a maar forms
Maars are shallow craters formed by phreatomagmatic explosions, which come from magma interacting with groundwater (here, permafrost). When magma gets close to permafrost it creates steam, which raises the volume and builds pressure until it is released in a violent explosion. The eruption throws out rock, magma and ash and leaves a ring of rock fragments and sediment around the crater. Over time maar craters often fill with water and become lakes.
The four are the Devil Mountain Maar Lakes, Whitefish Maar Lake, and North and South Killeak Maar Lakes. All are oval-shaped except the Devil Mountain Maar Lakes, which were created by multiple explosions during a complex eruption.
Maar locality. NPS graphic.
Why permafrost made them so big
NPS says permafrost, the permanently frozen ground, is the culprit for the unusual size. While the maars formed, the permafrost was about as thick as the length of a football field. Because ice needs two to three times more energy than liquid water to become steam, thick permafrost gave a large reservoir of fuel that fed each explosion a little water at a time. Phreatomagmatic eruptions with low water-to-magma ratios are the most explosive. With liquid water the most explosive phase typically comes early, when the groundwater is still low, or near the end, when the water supply is nearly used up. At the Espenberg Maars, the high energy needed to melt ice kept the water-to-magma ratio low throughout, and the abundance of ice supplied plenty of water. The result, NPS says, was prolonged and highly explosive eruptions.
Rock from below
The explosions turned the earth inside out. The lakes are ringed by fragments of older rocks and sediments from the layers beneath them. At Devil Mountain Maar, the fragments include quartz and schist from the Paleozoic basement rock, Eocene volcanic rocks from older eruptions in the region, and Pliocene and Pleistocene sedimentary rocks and sediments. NPS calls the tephra deposits around the maars an array of rocks of different ages and the maars themselves a time capsule.
The four lakes
| Lake | Age | Size |
|---|---|---|
| Devil Mountain Maar Lake | About 17,500 years, the youngest | Nearly 5 miles long, 3.7 miles wide, 328 feet deep |
| South Killeak Maar Lake | Over 40,000 years | Just over 3 miles long, nearly 200 feet deep |
| North Killeak Maar Lake | 50,000 years | 2.5 miles in diameter, 80 feet deep |
| Whitefish Maar Lake | Estimated 100,000 to 200,000 years, the oldest | Just over 2.5 miles long, depth not measured |
Devil Mountain Maar Lake is formed by a northern and a southern crater separated by a small spit. At the water's edge, a bedrock cliff the height of 15 stories surrounds it.
Devil Mountain Maar Lake in spring. NPS photo.
NPS notes that a piece of petrified wood was discovered around Devil Mountain Maar Lake. It dates from a time when this part of the world was warmer and could support large vegetation.
Petrified wood from Devil Mountain Maar Lake. Image from NPS's page.
Water meets land along South Killeak Maar Lake. NPS photo.
Whitefish Maar Lake. NPS photo.
Sources
- National Park Service, Bering Land Bridge National Preserve, "Bizarre Maars," https://www.nps.gov/articles/bizarre-maars.htm; the page cites Hopkins (1988) and Beget, Hopkins and Charron (1996); rewritten in hubnx's own words.
In these publicationsBering Land Bridge National Preserve
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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