Basalt Flow in Glacial Outwash - Yellowstone National Park
February 03, 2004
The photo above was taken this past June in Yellowstone Park, and although it's just a stop along the road between the advertised geothermal features, it's impressive nonetheless. The orderly columns across the lower center of the picture are volcanic in nature. Several million years ago, from vents in the Yellowstone Plateau, lava covered the region in a vast molten flood 25 feet (8 m) deep. As the lava cooled and contracted, about 1.3 million years ago, it formed contraction cracks, producing hexagonal columns of basalt. Above and below the basalt lies a loose mix of gravel carried here by glacial meltwater. This basalt column extends all of the way across the canyon. See also the Earth Science Picture of the Day for July 17, 2003.