Vents, of course, are the locations from which lava flows and pyroclastic material are erupted. Their forms and orientations can be used to determine many characteristics of the eruption with which they were associated. There are two main endmembers in a spectrum of pyroclastic vents in Hawai'i, spatter vents and cinder cones. Their differences are due mostly to the gas content of the magma that is erupted. Additionally, there are satellitic shields formed during eruptions without fountaining and tuff cones formed during phreatomagmatic eruptions.

As a dike approaches the surface, it generates a zone of tension at the surface. This tension is usually manifested as a pair of cracks with the ground in between sometimes dropped down a little. The first phase of a Hawaiian eruption is usually characterized by breaking to the surface of a dike along one of the two fractures resulting in a line of erupting vents commonly called a "curtain of fire" (e.g. Macdonald 1972). After a few hours or few days most parts of the fissure stop erupting and activity is concentrated at one or more separate vents (e.g. Bruce & Huppert 1989). It is these vent locations that usually persist long enough (hours to weeks and sometimes years) to produce significant near-vent constructs. The change from long continuous erupting fissures to one or a few vents must be remembered when mapping eruptive fissures in remote sensing data and relating them to dike dimensions: The near-surface part of the dike is almost certainly longer than any line of near-vent constructs (see discussion in Munro 1992).

Spatter vents
Cinder cones
Satellitic shields
Phreatomagmatic vents


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