Читать книгу One Best Hike: Grand Canyon. Everything You Need to Know to Successfully Hike from the Rim to the River—and Back онлайн

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The final big event required for the creation of the modern Colorado River course is the creation of the Gulf of California, which occurred about 6 million years ago, and provided the Colorado River’s outlet to the ocean.

Glaciations and fault movements, 6 million years ago to present: By 6 million years ago, the Colorado River followed its current course to the Gulf of California. Events during the past 2 million years contributed to significant downward erosion, allowing the canyon to achieve its depth. First, the past 2 million years have been a time of recurring glaciations and at the end of each glacial cycle, greatly increased runoff from the Rocky Mountains would have resulted in giant floods with enormous erosive power.

Second, the Colorado River is crosscut by multiple faults, where the side of the fault that descends coincides with the downhill side of the river. Each time the fault moved, the downhill side of streambed would suddenly have been lowered, creating a step termed a knickpoint. A river’s erosive power slowly moves knickpoints upstream, in the process deepening the riverbed.