Historical Geology Understanding Our Planet\'s Past

the ocean floor more than 90 million years ago, when a series of volcanic

eruptions released immense quantities of basalt onto the Antarctic plate. The

timing also coincided with a mass extinction of species.

Prior to the opening of the Red Sea and Gulf of Aden, massive floods

of basalt covered some 300,000 square miles of Ethiopia, beginning about 35

million years ago.The East African Rift Valley extends from the shores of

Mozambique to the Red Sea, where it splits to form the Afar Triangle in

Ethiopia.For the past 25 to 30 million years, the Afar Triangle has been stew-

ing with volcanism. An expanding mass of molten magma lying just beneath

the crust uplifted much of the area thousands of feet.

In North America,major episodes of basalt volcanism occurred in the

Columbia River Plateau, the Colorado Plateau, and the Sierra Madre region.

A band of volcanoes stretching from Colorado to Nevada produced a series

of very violent eruptions between 30 million and 26 million years ago. Begin-

ning about 17 million years ago and extending over a period of 2 million

years, great outpourings of basalt covered Washington, Oregon, and Idaho, cre-

ating the Columbia River Plateau (Fig. 180). Massive floods of lava enveloped

Figure 179The Deccan
Traps flood basalts in
India.

Historical Geology

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