 Basalt lava erupts from Pu`u `O`o spatter and cinder cone at Kilauea Volcano, Hawaii. Lava spilling from the cone has formed a series of `a`a lava channels and flows. |
Effusive eruption
An eruption dominated by the outpouring of lava onto the ground is often referred to as an effusive eruption (as opposed to the violent fragmentation of magma by explosive eruptions). Lava flows generated by effusive eruptions vary in shape, thickness, length, and width depending on the type of lava erupted, discharge, slope of the ground over which the lava travels, and duration of eruption. For example, basalt lava may become `a`a or pahohoe, and flow in deep narrow channels or in thin wide sheets. Andesite lava typically forms thick stubby flows, and dacite lava often forms steep-sided mounds called lava domes. |
 |
Mauna Loa Volcano, Hawaii Lava erupts from a fissure high on the northeast rift zone of Mauna Loa (about 3400 m) on the morning of March 25, 1984. Fountains are 10 to 50 m high along the fissure, and lava output is estimated at 1-2 million m 3 /hour. This fissure fed a narrow `a`a lava flow that moved only about 5 km downslope (lower right) before new vents became active farther downrift. See eruption summary from the USGS Hawaiian Volcano Observatory for more information and images about the 1984 eruption of Mauna Loa. . |
 |
Colima Volcano, Mexico A stubby andesite lava flow advances 900-1,200 m down the southwest side of Colima Volcano. Lava was first observed in the summit crater on November 20 and began spilling over the crater rim the next day. Colima Volcano is the most historically active volcano in Mexico. For more information about Colima, see the volcanic activity reports provided by the Smithsonian Institution's Global Volcanism Program |
 |
Obsidian flow, Long Valley Caldera, California. Viscous rhyolite lava was erupted to form several circular-shaped lava flows, often referred to as domes, following a series of explosive eruptions from the Mono-Inyo Volcanic Chain. The eruptions occurred about 550-650 years ago. Obsidian flow (foreground) is about 1.5 km wide (left to right). A smaller lava dome, Wilson Butte, was erupted about 1,400 years ago (left of Obsidian flow), also following a series of explosive eruptions. |