Snake River Plain EarthCache
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The Snake River Plain is traversed by Interstate Highways 15, 86, and 84, plus a relatively good network of US, State, and County roads.
The Snake River Plain is a geologic feature located primarily in the American state of Idaho. It stretches about 400 miles westward from northwest of the state of Wyoming to the Idaho-Oregon border. The plain is a wide flat bow-shaped depression, and covers about a quarter of Idaho. The Snake River Plain represents a style of volcanism between flood basalt eruptions and Hawaiian volcanism. Like Hawaiian volcanism, plains volcanism involves multiple, thin (3-5 meters) flow units erupted from central vents, and minor fountaining to produce cinder cones. However, like flood basalt eruptions, the vents are often aligned on rift zones, and some of the flows are fissure fed. The surface of flow accumulation is planar, because the vents are spread over a wide area, not focused in a central zone. Typical of plains volcanism, most flows on the Snake River Plain accumulate as (1) small, low shields, (2) fissure flows, and (3) or large tube-fed flows. All were probably emplaced relatively slowly, often advancing only a few meters per hour, forming "toey" lava flows with hummocky surfaces of several meters relief. Pressure ridges and collapse craters are common. Much of the volcanism of the Snake River Plain was confined to volcanic rift zones. A volcanic rift zone is a concentration of volcanic landforms and structures along a linear zone of cracks in the earth's crust.
One explanation for the existence of the Snake River Plain and the Craters of the Moon lava field is called the mantle plume theory. This theory states that beneath the crust of the Snake River Plain lies a "hot spot" or localized heat source. Periodically, this hot spot consists of a "plume" of molten rock (magma) which rises buoyantly to the surface of the earth. The hot spot does not move but rather remains in a fixed position. What does move is the crust of the earth; as the North American plate slides southwestward over the hot spot. As the plate moves over the hot spot volcanic eruptions occur on the surface. Initially these eruptions are very violent and produce a lava known as rhyolite. Huge calderas of up to 30 miles in diameter are formed when these devastating eruptions take place. Later a more fluid lava known as basalt flows onto the surface and covers the rhyolitic flows.
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