| 翻訳と辞書 |
| Bonneville flood ： ウィキペディア英語版 |
Bonneville flood
The Bonneville flood was a catastrophic flooding event in the last ice age, which involved massive amounts of water inundating parts of southern Idaho and eastern Washington along the course of the Snake River. Unlike the Missoula Floods, which also occurred during the same period in the Pacific Northwest, the Bonneville flood only happened once. The flood is believed to be the second largest in known geologic history.
==Cause and events==
About 14,500 years ago, pluvial Lake Bonneville in northern Utah reached its highest water level since its formation. The lake occupied the present-day basin of the Great Salt Lake, except it was far larger, covering about . As it rose the lake level caused seepage at, then breached, the ancient level of Red Rock Pass, a mountain pass at the headwaters of the Portneuf River, a tributary of the Snake River above present-day American Falls Reservoir. Ancient Red Rock Pass was the site of two alluvial fans descending from opposite sides of the notch, forming a natural dam. The roughly -high flood crest raced down the Portneuf River valley, and eroded away a lava dam that previously was at the site of the present-day American Falls, releasing a -long lake, American Falls Lake, that had formed behind the natural dam.
At the peak of the flood, approximately poured over the Snake River Plain at a speed of per hour and deposited hundreds of square miles of sediments eroded from upstream. The flood scoured the -deep Snake River Canyon through the underlying basalt and loess soil, creating Shoshone Falls and several other waterfalls along the Snake River. It also carved and increased in size many other tributary canyons, including those of the Bruneau River and Salmon Falls Creek. Eventually, water also spilled down the Bear River into the plain. The flood then entered Hells Canyon, significantly widening the gorge. Its waters eventually reached the Pacific Ocean via the Columbia River.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「Bonneville flood」の詳細全文を読む
スポンサード リンク
| 翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|