Volcanic Rocks (Volcanic Products and Features)

摘要

Volcanoes have contributed significantly to the formation of the surface of the planet. Volcanism produced the crust we live on and most of the air we breathe. Often the remnants of an eruption are as revealing as the eruption itself, for they tell us many things about the eruption. Products of explosive eruptions include pyroclastic (fire broken) rocks and rock fragments. The force that produces explosive eruptions is the release of trapped gas. Ejecta from these explosions may be derived from the magma or from rocks in the vicinity of the volcanic conduit that are blasted out in the eruption. These may be ejected more or less vertically, then fall back to earth in the form of ash fall deposits. Pyroclastic flows result when the eruptive fragments follow the contours of the volcano and surrounding terrain. They are of three main types: glowing ash clouds, ash flows, and mudflows. Volcanic structures can take many forms. A few of the smaller structures built directly around vents include cinder, spatter, and lava cones. Thick lavas may pile up over their vents to form lava domes.