Bizarre Maars

Aerial view of North and South Killeak Maar Lakes.

NPS Photo

Magma and ice seem like an unlikely pair. Yet when mixed together they create amazing formations.

Maars are shallow craters formed by phreatomagmatic explosions: interactions between magma and groundwater (in our case permafrost). As magma comes into close proximity with permafrost it creates steam, thus, increasing its volume and building pressure until it is released through a violent explosion. This eruption ejects rock, magma, and ash and creates a ring around the crater made of rock fragments and sediment ejected from the earth. Over time, maar craters often fill in with water and become lakes.

The four Espenberg Maars are located near the northern boundary of Bering Land Bridge National Preserve and are unique for their location and size. Not only are they the largest maar lakes in the world, but they are also the most northerly located volcanic features in North America created during the Ice Age. They include Devil Mountain Maar Lakes, Whitefish Maar Lake, and North and South Killeak Maar Lakes. All are oval-shaped except for the Devil Mountain Maar Lakes, which were created by multiple explosions during a complex eruption. The culprit for their unusual large size is the permafrost or permanently frozen ground.

Maar locality

NPS graphic

During the formation of the maars the permafrost was about as thick as the length of a football field. Ice requires about two to three times more energy than liquid water to convert it into steam and cause a phreatomagmatic explosion. A thick layer of permafrost provides a large reservoir of fuel to feed the explosion a little water at a time. It so happens that for optimal explosion potential, phreatomagmatic eruptions with low water to magma ratios do it best. During phreatomagmatic eruptions with liquid water, the most explosive phase typically occurs early in the eruption when initial groundwater is low or towards the end of the eruption when water supplies have been nearly exhausted. In the case of the Espenberg Maars, the high-energy demands of melting ice kept water to magma ratios continuously low and the abundance of ice provided an ample supply of water, resulting in prolonged and highly explosive eruptions.

Geological timeline featuring the Palaeozoic to the Caenozoic era.

These eruptions turned the Earth inside out. The lakes are surrounded by fragments of older rocks and sediments from the depths of the Earth. The older rocks and sediments ejected from the maars are sourced from the layers of earth lying below the Espenberg maars. At the Devil Mountain Maar, rock fragments include pieces of quartz and schist sourced from the Paleozoic basement rock, Eocene volcanic rocks formed by older eruptions in the region, and Pliocene and Pleistocene sedimentary rocks and sediments.

This is amazing stuff! An array of variously aged rocks lie at your feet in the tephra deposits around the maars. Maar formations are nature’s time capsule. They are coffers holding the secrets of Earth’s past.

Devil Mountain Maar Lake in spring.

NPS photo - Jim Pfeiffenberger

Devil Mountain Maar Lake

Devil Mountain Maar Lake is formed by a northern and a southern crater, which are separated by a small spit. It is the youngest of all the Espenberg maars and formed about 17,500 years ago. It is nearly 5 miles long and 3.7 miles wide, and is 328 feet deep. When standing at the water’s edge, a 15-story bedrock cliff surrounds the Devil Mountain Maar. It may be truly hard to imagine the energy it took to create such a large depression.

Petrified wood from Devil Mountain Maar Lake.

A petrified peice of wood was discovered around Devil Mountian Maar Lake. This piece of wood originated from a time when this part of the world was warmer and could support large vegetation.

View a 3D model of the petrified piece of wood.

Water meets land along South Killeak Maar Lake

NPS Photo - Jim Pfeiffenberger

North and South Killeak Maar Lakes

South Killeak Maar is over 40,000 years old, is just over 3 miles long and has a depth of nearly 200 feet. Its counterpart North Killeak Maar is slightly older at 50,000 years old with a diameter of 2.5 miles and a depth of 80 feet.

Whitefish Maar Lake

NPS Photo - Jim Pfeiffenberger

Whitefish Maar

Whitefish Maar is the oldest, estimated to be 100,000 – 200,000 years old. It is just over 2.5 miles long. Its depth has not been measured.

Bibliography

Hopkins, D. M. (1988). The Espenberg Maars: A record of explosive volcanic activity in the Devil Mountain – Cape Espenberg area, Seward Peninsula, Alaska. Bering Land Bridge National Preserve: An Archeological Survey Volume 1, 262-321.

Beget, J. E., Hopkins, D. M., Charron, S. D. (1996). The Largest Known Maars on Earth, Seward Peninsula, Northwest Alaska. Arctic Volume 49(1), 62-69.