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USGS CMG InfoBank: Rift Zone

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Comment: 02:59 - 04:01 (01:02)
Source: Annenberg/CPB Resources - Earth Revealed - 6. Plate Dynamics
Keywords: "plate tectonics", "convergent plate margin", Iceland, "mid-Atlantic ridge", "mid-oceanic ridge", rift, landscape, earthquake, geyser, "hot spring", crust, "lava flow", "volcanic ash", basalt, fissure, volcano, plate, magma, "divergent plate"

Our transcription: In few places can one see a plate boundary better exposed than in Iceland atop the mid-Atlantic ridge.
In a broad zone across Iceland, great tensional cracks called "rifts" break the landscape.
Frequent small shallow earthquakes occur beneath this rift zone.
Geysers and hot springs are evidence that the crust is hot.
From time to time, great volumes of fluid basaltic lava and ash spew from fissures and volcanic craters.
Here the crust is being pulled apart as basaltic magma fills the fissures that open, it solidifies, adding new crust to the edges of the plate.
As the older rock is pulled away, new magma rises to cool, harden, and form additional crust in its place.
This type of boundary is called a "divergent boundary" for here the plates separate from one another.

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Page Last Modified: Thu Oct 31 04:25:45 PDT 2013  (chd)