#flood basalt

Basalt Wall, Palouse River Canyon, Franklin County, 2015.

Latourell Falls

The Columbia River Gorge has an incredible geologic history. The rocks that make up its walls are the result of a huge outpouring of lava in the Miocene, about 15-20 million years ago. The Columbia River Flood Basalts covered large portions of Washington and the Northern Oregon, possibly due to a plume of hot mantle material hitting the bottom of the continent.

The Gorge was then carved by the Columbia River over a period of a few million years. The river cut downwards, removing the igneous rocks with the aid of a few catastrophic events. A huge lake called Glacial Lake Missoula formed during the last glacial period; edges of the ice cap trapped a huge lake of melt-water behind them. When the water overtopped the ice, it melted the dam and produced an instant, catastrophic flood that eventually reached the Columbia River. That flood repeated at least several dozen, if not more than 100 times, carving the gorge even deeper.

The vertical shaft of water that is Latourell Falls is the closest waterfall to the city of Portland along the river gorge. Here it is capture almost perfectly, appearing as a vertical shaft of light. The igneous rocks that surround it show spectacular columnar jointing; a fracture pattern produced as lavas cool and shrink due to thermal contraction.

-JBB

Image credit: Kirk & Barb Nelson https://flic.kr/p/oB15DR

Waterfall bisected by fault.

If it weren't for their relative proximity to Iguazu the Saltos de Mocona, located near El Soberbio in Argentina's Missiones province, would be more famous. As the Rio Uruguay flows over the same flood basalts one sees at Iguazu (for the geology see our past post at http://tinyurl.com/mury9vx), a fault runs down the length of the river, leaving a three km long waterfall that drops between15 and 25 metres across the fault. The river marks the border with Brazil and the area is covered in dense dark green woodland forming provincial parks and biosphere reserves on both sides of the invisible line.

The falls sideways into a gorge, and the water level needs to be just right for best effect. Too low and the water all falls into the gorge, too high and the fault is covered by the river, but just in between, this spectacular wonder of nature appears. The name is Guarani, an autochthonous language still spoken in the region, and means 'he who swallows everything'. They have been declared a national monument, and the park contains over 2,000 species of plant, a huge variety of brightly coloured butterflies (I counted over 40 kinds in a morning) and a variety of animals, including toucans and coatimundis.

Loz

Image credit: Ministerio de tourismo Argentina.

http://www.worldwaterfalldatabase.com/waterfall/Mocona-Saltos-del-5477/