The first thing people most people notice about basalt is its very dark color. Basalt has lots of iron and magnesium-rich minerals that give it its distinctive, almost black color. The second thing people most people notice about basalt along the Lava Flow trail is its bubbly texture. Geologists call these small bubbles vesicles. They can be found in any type of volcanic rock.
Vesicles are evidence that the basaltic lava had plenty of gas.
Given enough time, the gas will its way out of the lava and escape into the air. These gas bubbles were frozen into place before they could escape. This site is a cooperative endeavor of the US Geological Survey Western Earth Surface Processes Team and the National Park Service .