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Free Picture: Tweed Extinct Volcano, Australia
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Description
Australia is the only continent without any current volcanic activity, but it hosts one of the world's largest extinct volcanoes, the Tweed Volcano. Rock dating methods indicate that eruptions here lasted about three million years, ending about 20 million years ago. Twenty million years of erosion has left this landform deeply eroded yet very recognizable, appearing as a caldera with a central peak. The central peak is not an old remnant landform but is instead the erosional stub of the volcanic neck (the central pipe that carried the magma upward). It is surrounded by ring dikes, which are circular sheets of magma that solidified and now form erosion-resistant ridges. The central peak is named Mount Warning. Topography plays a central role in envisioning the volcano at its climax and in deciphering the landscape evolution that has occurred since then. Low-relief uplands interspersed between deeply eroded canyons form a radial pattern that clearly defines the shape and extent of the original volcanic dome. Erosion is most extensive on the eastern side because the eroding streams drained directly to the ocean and therefore had the steepest gradients. This asymmetry of erosion has been extreme enough that the volcano has been hollowed out by the east-flowing drainage, forming an "erosional caldera". Calderas usually form as the result of collapse where magmas retreat within an active volcano. If collapse occurred here, erosion may have removed the evidence, but it produced a similar landform itself.
Keywords
australia, caldera, earth science, geography, jpl, mount warning, nasa, topography, tweed volcano, volcano, volcanoes, tweed extinct volcano, free photography, free photo, free photos, free picture, free pictures, free image, free images
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