(Tachylites) are Unusual and Unique
The Menan Buttes are extinct volcanoes formed by violent eruptions 10,000 years ago. Unusual because they erupted through the cold waters of the Snake River that flowed where the buttes stand today. When molten magma met the cold river water, it cooled so quickly crystals were unable to form and the lava solidified into glass called tachylite. The heat of the magma flashed the river water to steam, shattering the magma into tiny fragments that welded together as the hot ash settled to the ground into glassy rocks. North Menan Butte is a National Natural Landmark because the buttes are the only volcanoes in the United States to erupt through freshwater.
Spaces left by gas bubbles in hot lava as it surfaced, cooled and solidified from the vent of the North Menan volcano.