Looking NNW across Molina Crater (foreground) and MacDougal Crater, two maars at the NW edge of the Pinacate volcanic field. Eruptions at Molina Crater were from several vents. Pinacate maars formed chiefly by collapse when rising basalt magma encountered groundwater at depth and flashed it into steam. This drove explosive eruptions that ejected fragments of old basalt flows, bits of fresh magma, and unconsolidated sediment in various proportions.