Lava plateaus form through repeated, quiet eruptions of highly fluid basaltic lava from multiple vents over extended periods.
Here's a breakdown of the process:
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Basaltic Lava: The lava involved is primarily basaltic, meaning it has a low viscosity (it flows easily). This low viscosity is crucial because it allows the lava to spread over vast distances.
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Quiet Eruptions: Unlike explosive volcanic eruptions, these eruptions are "quiet" or effusive. This is because the lava has a relatively low gas content. When gas content is present, it escapes easily due to the lava's low viscosity, preventing pressure build-up.
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Multiple Vents: The lava doesn't typically erupt from a single central vent like a volcano. Instead, it emerges from numerous fissures or cracks in the Earth's surface.
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Successive Eruptions: The key to plateau formation is the repetition of these quiet eruptions. Over time (often millions of years), layer upon layer of basaltic lava is added, creating a thick, extensive plateau.
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Spreading and Solidification: The highly fluid lava flows far from the vents, cooling and solidifying into broad, flat sheets.
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Formation of Stepped Topography: These successive lava flows accumulate to form a large, elevated plateau. Erosion can further sculpt the edges, creating a stepped or terraced appearance.
Example:
A prime example of a lava plateau is the Columbia River Plateau in the northwestern United States. This plateau was formed by extensive basalt flows that occurred over millions of years.
In summary, lava plateaus aren't formed by a single volcanic event, but rather by the accumulation of many layers of fluid basaltic lava over long geological timescales through non-explosive eruptions.
