Espenberg Maars

A maar is to a volcano as is an inverted mole hill to a mountain. It's an eruption that started off with a bang but then ran out of steam and sort of collapsed back into itself.

A maar forms when a pipe of molten lava eats its way up from the depths to breach the ground surface. In most or all instances there is a violent initial explosion just as the maar vents to the surface. This explosion occurs when steam is formed by the molten rock contacting near-surface ground water. Then the resulting steam pressure becomes great enough to blow away the overlying rocks.

Early inhabitants of the Seward Peninsula had several opportunities to see maars form. These maars were created on the low plain between Shishmaref and Cape Espenberg at the northeast tip of the Seward Peninsula, just across the sound from Kotzebue. One maar formed about 9,300 years ago. Another erupted 13,000 years ago, and others were created as early as 200,000 years ago.

All that remains today are the shallow, near-circular lakes that are characteristic of maars. Typically, maar eruptions belch steam, smoke and rocks only for a few days and then they grow quiescent and the vents fill with water to form permanent lakes.

That the lakes near Cape Espenberg are truly of eruptive origin is demonstrated by the rocks found around the rims of the water-filled craters. These rocks are conglomerations of volcanic ash and soil and also pieces of subsurface rock broken away from the pipe wall and carried up along it to be forcibly ejected onto the rim.