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Why is heat flow especially high near mid-ocean ridges?
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oceanic crust
A cross section of Earth's outer layers, from the crust through the lower mantle.
Heat flow is exceptionally high near mid-ocean ridges primarily because these areas are the sites of seafloor spreading, where molten material from Earth’s mantle continuously wells up to create new oceanic crust.31
The anomalously high heat flow—which can measure three to four times the global average—is attributed to the intrusion of this hot, molten magma near the ridge crests. This upwelling process also causes the crust to be "swollen" with heat, which results in the elevated topography characteristic of oceanic ridges. As the newly formed crust moves away from the spreading center, it undergoes thermal contraction and cools, which explains why the seafloor depth increases with the age of the crust.123