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How does basalt form the upper layer of oceanic crust?
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oceanic crust
A cross section of Earth's outer layers, from the crust through the lower mantle.
The upper layer of oceanic crust, which is approximately 500 metres thick, is formed through volcanic activity at spreading centres along oceanic ridges.1
This process occurs as magma rises from the asthenosphere to the seafloor. The magma travels through a "plumbing system" of subvertical dikes before erupting onto the surface. These eruptions produce basalt in two primary forms:12
- Pillow lavas: These form small, rounded hills and are shaped like large, overstuffed pillows.1
- Sheet flows: These appear as thin, wrinkled layers and are believed to be erupted at higher temperatures than pillow lavas.1
As tectonic plates diverge, these basaltic lavas flood the rift valley, building volcanoes and creating the uppermost layer of the crust. Over time, this material becomes the ocean floor, upon which sediments are eventually deposited.3