Photographer: Marcus Moore

Summary Authors: Marcus Moore; Jim Foster

The photo above shows a rock outcrop composed of two rhyolitic magmas that mixed during a volcanic eruption in the year 1350. It was taken at Glass Creek Dome, California. The mixing is best seen at the center of the rock, where darker colored obsidian flows around the lighter colored pumice. Rhyolitic magmas form at relatively cool temperatures (650 to 800 C or 1200 to 1470 F) but tend to have a high gas content and high viscosity -- 1 million and 100 million times more viscous than water. Compared to other types of magma they're also rich in feldspar. Photo taken on July 14, 2018.

Photo Details: Camera: Apple iPhone 6s; Exposure Time: 0.0083s (1/120); Aperture: ƒ/2.2; ISO equivalent: 25; Focal Length (35mm): 29.