Explosive hydrovolcanic eruption plumes commonly collapse to form base surges that spread outward from the base of the eruption column. Base surge at Capelinhos, Azores, 1957. Nonexplosive lava flows under water commonly form pillow lavas or fragmental pillow breccias. The interactions produce fragments known as hydroclastites. Jurassic pillow basalt at Avila Beach, California.
Subaqueous explosions result from magma-water reactions in shallow water bodies or beneath ice.
Littoral explosions occur where subaerial lava flows or hot pyroclastic flows intersect with water along shorelines. Littoral cones are formed at the edge of the sea from lava entering the water. Various kinds of explosive hydroclastic processes generate maar volcanoes, low-rimmed craters. Rim beds inside maar crater, Ukinrek volcano, Alaska. Arrow points to Dr. Michael Ort, Northern Arizona University, rappeling down crater wall to investigate origin of beds.