Fulgurite

October 26, 2010

Fulgurite 
Photographer: Stan Celestian; Stan's Website
Summary Author: Stan Celestian; Jim Foster

October 2010 Earth Science Picture of the Day Viewer's Choice

Fulgurites may be produced when a cloud-to-ground lightning bolt penetrates soil, most often sandy soil. Within a second or two, the intense heat of the lightning vaporizes and or melts any particles in its path. Sand grains that have melted will quickly cool to a glassy substance that acts to cement additional particles coming in contact with it. The shape of the fulgurite typically resembles that of a root system -- a lightning strike takes multiple routes to dissipate its energy. Temperatures of approximately 3,270 degrees F (1,800 C) or higher are required for the formation of fulgurites. 

The above specimen was found near Queen Creek, Arizona. It's about 14 inches (35.56 cm) in length, and the thickest part of the “stem” is about 2 inches (5 cm) in diameter. The right side of this fulgurite was exposed at the surface -- its branching sections extended into the soil. Brushing the loose soil away exposed the delicate tendril structure. Photo taken on May 4, 2005.

Photo details: Camera Maker: NIKON CORPORATION; Camera Model: NIKON D70; Focal Length: 60mm (35mm equivalent: 90mm); Aperture: f/14.0; Exposure Time: 0.100 s (1/10); Exposure Bias: none; Metering Mode: Matrix; Exposure: aperture priority (semi-auto); White Balance: Manual; Light Source: Incandescent; Flash Fired: No; Color Space: sRGB.