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How can hot material rising in the asthenosphere form a plateau?

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plateau The Columbia Plateau is uniformly covered with basaltic lava flows and spans an area of about 100,000 square miles in Idaho, Washington, and Oregon.

Hot material rising in the asthenosphere can form a plateau through the process of thermal expansion of the lithosphere.1

When hot material upwells from the asthenosphere beneath a broad region, it rapidly heats the overlying lithosphere. This warming causes the uppermost mantle to expand, which results in the uplift of the surface above it. If the area was previously low-lying and lacked significant relief, the surface tends to remain relatively flat as it is raised to a higher, uniform elevation.1

This mechanism is a primary factor in the formation of high plateaus, such as those found in Ethiopia and parts of East Africa. While these plateaus are sometimes associated with volcanism or rift valleys, these features are not required for the plateau to form; the essential process is the thermal heating and subsequent buoyant uplift of the lithosphere.1