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‘ā or pāhoehoe, 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.

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