Craters of the MoonSnake River Plain, Idaho
The vast volumes of lava you can observe in Craters of the Moon came from a system of long crustal fractures forming a series of volcano across the Snake River plain. The vegetation is still very sparse due to the relative recent volcanic history. Eruptions occurred between 15,000 to 2,000 years ago. The dry climate of eastern Idaho offers limited erosion and lava rocks have yet to be transformed into a soil.
The Pahoehoe flow (on the left), spilled from the North crater vent 2,200 years ago. This kind of flows often occur with well insulated underground tube system that carries the lava over long distances, with limited cooling. Pahohoe has a smooth ropy surface and more vesicles than the surrounding `a`a lava with its rough, jagged and clinkery surface. Lava transported at surface in open channels has less time to cool down which allows the trapped gas to escape.
When the pressure in the lava tube is sufficient, squeeze-ups may occur. The lava rise up the tension in fractures. Lava fountains erupt from the elongated fissures and form spatter rampart.