Tuesday, June 18, 2013

Idaho’s rugged sea of basalt


A rugged sea of over 60 different basaltic lava flows stretches over the Snake River Plain in southern Idaho. Also known as Craters of the Moon, the lava plain formed between 15,000 and 2000 years ago during 8 eruptive phases. In between these phases quiet periods could last up to 3000 years. Nowadays you can see rivers of lava, ropy & blocky pahoehoe lava flows, deepcracks, cinder & spatters cones and a labyrinth of lava tube tunnels under the surface. During an eruption basalt would flow around higher outcrops also known as kipukas. Some of these contain 700-year old juniper trees and braches of sagebrush giving them the appearance of an isolated island. Precipitation is lost in the deep cracks of the basalt and oozes out at the nearby Snake River Canyon.

Volcanism at Craters of the Moon is connected to the Great Rift, a linear volcanic zone of fissures and vents (or a weak spot in the earth’s crust) over 100km in length from which basalt oozes quietly. In this way fast flowing lava is deposited and appears as a flowing river. The great rift contains one of the deepest open rift cracks in the world, at 240m. Another explanation for the volcanism at Craters of the Moon is the mantle plume theory. This theory states that the hotspot that now lies under Yellowstone National Park can be traced back to the Snake River Plain (and also the Colombia River plain). The eruptions connected to Yellowstone are however much more violent and associated with ryolithic lava and caldera forming.

The Snake River plain has been inhabited by indigenous tribes for at least the last 14,000-12,000 years. At the northwestern edges of the lava plain seasonal campsites (indicated by the presence of flint and obsidian tools) were discovered by archaeologists. Yet, there is also some evidence that tribes roamed the rugged and inhabitable lava flows. Here, stone piles and circles marked routes of trails but also cave entrances and sources of water.

A Shoshone-Bannock myth mentions the creation of the lava field. A huge serpent supposedly lived on the Snake River Plain and after a long winter it decided to get some sun by curling itself around a mountain. Soon thunder and lightning started circling the mountain angering the snake who tightened its grip on the mountain with so much force that stone began to melt and fire came from fissures in the ground. As a slow animal the snake could not get away, died and became covered in molten rock. Hence, the name Snake River Plain. Today you can still see the snake's shape in the solidified rock.

A more recent story called ‘’Lost Valley of The Lavas’’ tells the story of band of Shoshone tribes disappearing in the lava field during war only to reappear again in perfect health. According to the European settlers the tribes hid food in the cracks and drank from underground water supplies.


Image: NASA Earth Observatory. A true image Landsat image showing the Pioneer Mountain in the upper right and the craters of the moon to the northeast.

References:

http://earthobservatory.nasa.gov/IOTD/view.php?id=3964

http://www.nps.gov/crmo/index.htm

http://vulcan.wr.usgs.gov/Volcanoes/Idaho/CratersMoon/description_craters_moon.html

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