A geologist is working in an area of old volcanic rocks exposed by erosion. He finds a large rock outcrop that contains flat lying gravels in the base of the outcrop

These gravels are overlain by basalt that forms a series of layers representing flows. The uppermost basalt lava flows have a dip of about 10 degrees to the west. What does this outcrop record?
A) Gravels were initially deposited in a river valley and a cinder cone was erupted, damming the valley, before a cinder cone formed.
B) Basalt flows formed after gravels were deposited, covered the local terrain, and built a shield volcano with dips of about 10 degrees.
C) Basalt flows formed above a series of gravels, filling a river valley.
D) You can't tell anything about the history of this region from this outcrop.


B

Environmental & Atmospheric Sciences

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