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35-Year Anniversary Of The 1987 Middle Brother Rockfall Today

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avatar 35-Year Anniversary Of The 1987 Middle Brother Rockfall Today
March 10, 2022 12:17PM
Today, March 10, marks the 35-year anniversary of the 1987 Middle Brother rockfall, one of Yosemite’s most notable historical rockfalls.

At 2:15 pm on March 10, 1987, Ranger Jim Tucker received word that a road crew working on Northside Drive below Middle Brother had witnessed several small rockfalls and heard cracking sounds coming from the cliff. Upon arrival, Tucker witnessed another small rockfall. Sensing a growing hazard, Tucker instructed the road crew to leave the area and ordered traffic stopped at Camp 4. Minutes later, at 2:47 pm, a huge slab of rock broke loose from the top of Middle Brother.

Trail Crew Foreman Jim Snyder and another ranger had set up a spotting scope in Leidig Meadow and were eyewitnesses to the event. Snyder described the cliff “unfolding like the stairs of an escalator” as the giant slab fell onto a prominent ledge and fragmented into thousands of boulders. As the boulders hit the base of the cliff, Snyder's companion yelled, “Run!” Snyder, wanting to run but also wanting to watch the event unfold, tried to do both until he and his companion were enveloped in dust and small rock fragments. Stumbling blindly, they made their way to back to Tucker, who was preparing to send out a search party. When the huge dust cloud finally cleared, nearly 200 feet of Northside Drive was covered in boulders and fallen trees.

The 1987 Middle Brother rockfall was once thought to be the largest historical rockfall in Yosemite but recent advances in photogrammetry allowed geologists to re-examine this. Comparing models of Middle Brother created from old photographs with recent laser scans shows that the rockfall volume was 20,193 cubic meters (713,110 cubic feet), much smaller than the original estimate and smaller than other historical rockfalls. Nevertheless, the 1987 Middle Brother rockfall is notable because of its still-impressive volume, its location directly above Northside Drive, and Ranger Tucker's decisive life-saving actions that day.

For more information on how geologists measured the rockfall volume, see "Quantifying 40 years of rockfall activity in Yosemite Valley with historical Structure-from-Motion photogrammetry and terrestrial laser scanning": https://www.nps.gov/yose/learn/nature/upload/Guerin-et-al-2020-Geomorphology-sm.pdf
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