● breach the surface, producing a tuff cone of consolidated volcanic ash
● form filled relatively shallow craters known as a maars
● form other volcanic pipes
The term diatreme sometimes refers to any concave body of broken rock or tuff-breccia, generally formed by explosive or hydrostatic forces, whether or not the structure is related to volcanism. Some diatreme, phreatic explosions result from the interaction of hot magma with relatively shallow groundwater.