Lithology Effect - Vesicular Basalt

Vesicular basalt is a very porous rock type.  Above the water table the pore space is filled with air allowing the surface temperatures to effect the rock temperatures deeper than normal.  Because cold air is more dense and sinks, it flows through the vesicular basalt causing the temperature to decrease with depth, rather increase in normal scenarios.  In a temperature curve the air effect appears as an exaggerated annual wave effect (in amplitude and depth). Typically these wells exhale and inhale air depending on atmospheric conditions. Temperatures below the water table are frequently disturbed by large amounts of water flow in the porous rocks.  One of the most likely places to find vesicular basalt is in the region of the Snake River.