Atami 2021: “The Mudslide Ruins Were the Largest I’ve Ever Witnessed”

You don’t expect your life to end suddenly on a rainy Saturday morning, puttering around at home. To have earth and water and debris careen down a slope and slam into, through your home. You barely have time to realize what’s happening. And then it’s over.

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High up in the hills above Atami, rainwater finished infiltrating the nearly 56,000 cubic meters of soil and debris that had been packed into the head of the valley. Unable to drain, the water instead saturated the fill, putting intense pressure on unconsolidated particles and causing the mass to lose its cohesion, a condition called static liquefaction.

No longer strong enough to win its battle against gravity, the mass abruptly slid downslope, into the stream channel. Beginning as a normal landslide, it rapidly transitioned into a channelized debris flow within the confining walls of the valley. It incorporated river water, trees, rocks, soil, and previous landslide deposits into itself, churning everything together into a dense, massive wall of destruction. Nothing could stop or slow it as it bore down upon Atami. And wherever it passed, devastation followed. (more…)