Devils Postpile

January 07, 2011

Photographer: Nel Graham
Summary Author: Nel Graham

January 2011 Earth Science Picture of the Day Viewer's Choice

Devils Postpile, shown above, is a well-known example of columnar basalt. This type of formation results from thick basalt flows that cool slowly from the top down, causing shrinkage cracks at roughly 120 degree angles to propagate from the top toward the bottom of the flow. At the base of the columns are a number of broken sections of the "posts," many of which are hexagonal, some with as many as seven sides. This region is part of the Long Valley Caldera, which erupted explosively about 750,000 years ago. The flow that produced the postpile occured sometime after the eruption. This area is still volcanically active and closely monitored by United States Geological Survey (USGS). Mammoth Mountain, a popular ski area, is located close by. Photo taken in the summer of 2008.

Photo details: Camera Maker: OLYMPUS OPTICAL CO.,LTD; Camera Model: C3100Z,C3020Z; Focal Length: 6.6mm; Aperture: f/4.0; Exposure Time: 0.0015 s (1/650); ISO equiv: 100; Exposure Bias: none; Metering Mode: Matrix; Exposure: program (Auto); Flash Fired: No; Color Space: sRGB.