A “tuff ring” is a small volcanic cone of low relief that surrounds a shallow crater. These craters, known as maars, are formed by explosions caused by hot magma coming in contact with cold groundwater. The explosion blasts fragments of bedrock, tephra, and ash from the crater. The tuff ring forms as these ejected materials fall back to Earth. Tuff rings range in size from several hundred meters across to several thousand meters. They are typically less than a few hundred meters in height and have a very gentle slope of less than ten degrees.