May 28, 2016 | David F. Coppedge

Giant Rockfall Enlarged Zion Canyon Recently

Within Bronze Age dates, a cataclysmic landslide enlarged Zion Canyon, forming a large lake.

Geological change can happen quickly. Picture enough material to cover New York’s Central Park with 275 feet of debris; that’s how much material fell from the walls of Zion Canyon about 4,500 years ago, according to estimates announced by PhysOrg. The Sentinel Slide began when a crack in the Navajo sandstone gave way.  The BBC News shows maps of the landslide’s progress over the next few moments.

“It’s a spectacular volume of material. You get, essentially, one of Zion’s most massive cliffs collapsing, running across the canyon in 20 seconds with peak velocities of 90 metres per second (200mph),” said Dr [Jeff] Moore [University of Utah].

Within 60-90 seconds, it was all over. The dust probably took a long time to settle. Flowing south, the Virgin River backed up behind the landslide, forming a lake that lasted for about 700 years before overtopping the debris and carving a channel out. During the lake period, sediments settled on the bottom, flattening the canyon floor and making it easy for today’s visitors to drive into the canyon. The remains of the Sentinel Slide begin south of Zion Lodge and continue downriver for two miles. Moore estimates its volume at 286 million cubic meters of debris.

Lake sediments formed the flat floor of Zion Canyon.

Lake sediments formed the flat floor of Zion Canyon. By David Coppedge, 2014

This is probably one of many landslides that created Zion Canyon, Moore believes. A smaller one in the northern regions of the park happened about 2,600 years ago. Moore dated the slide by measuring cosmic ray damage in the newly-exposed rocks. New slides could occur at any time, with catastrophic consequences for today’s visitors. Such an event is unlikely, however. If it did, there would be no warning. There is no evidence of an earthquake or other trigger for the Sentinel Slide.

This event is another example of a large, rapid geological change within historic times. Consider also the Gros Ventre slide near Yellowstone, the explosions of Santorini and Krakatoa, and the near-instant changes around Mt. St. Helens in 1980. We have eyewitness testimony for cases like this. From others, we can infer what must have taken place, such as at the Heart Mountain detachment east of Yellowstone, the Chile dam breach (2/18/16), the Channeled Scablands, and now Zion.

Creationists believe changes before, during and after the Flood differed only in scale. There’s no need for millions of years.

Project: At the rate of known catastrophes over the last 10,000 years or so, including all sources from tsunamis, volcanoes, landslides, megafloods and other rapid events, could any point on a continent expect to remain unmodified for millions of years?

 

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