Multnomah Falls

Multnomah Falls_n multnomah-falls 200px-Multfalls images

Multnomah Falls

The Columbia River gorge marks the border between Washington and Oregon states in the western USA, the latter side being graced with these spectacular spring fed falls that plummet a total of 190 metres in two major steps. They are the tallest in the state and one of the highest year round falls in the country. The water comes from percolating groundwater through nearby Larch Mountain, with additional contributions from rain and snow melt.

The rocks through which the gorge was cut are a part of the rising Cascade range, and composed of flood basalts that poured over 163,000 square km of the crust’s surface during the late Miocene and early Pliocene 17-14 million years back. An estimated 175,000 cubic km of magma erupted in less than three million years, in a series of distinct events (4 main ones are recognised), which finally petered out around 6 million years back. The crust sank beneath the weight of the lava forming the Columbia river plateau, forcing the water into its current course (the old one being buried under miles of lava).

The gorge was carved at the end of the ice age, when several huge releases from dammed lakes such as lake Missoula on the surface of the ice sheet eroded the scablands of the north American west. It is the only hydrological connection between the plateau and the Pacific ocean. A wide variety of ecosystems occurs as one journeys up from west to east. It began forming as the mountains rose, but was completed by the melted ice.
Source: The Earth story

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Violet Alex
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