53. the columbia plateau in the northwestern u. s. was constructed (built up by) a, a shield volcano b. repeated violent eruptions c. a series of fissure eruptions that released a huge volume of low-viscosity basalt flows d. a series of subaqueous lava flows

c. a series of fissure eruptions that released a huge volume of low-viscosity basalt flows

Explanation:

The Columbia Plateau in the northwestern U.S, commonly known as the Columbia Basalt Plain as well, is a pronounced geographic area located in the interior Columbia River Basin. It originated at a point between six million and sixteen million years ago due to a series of flows of basalt.

hi there!

the answer you are looking for is relatively steep.

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