Science Seminar: Earth Science

News about Landslides and Mudslides, including commentary and archival articles published in The New York Times.

IN the year since 43 people died in a landslide in Oso, Wash., we have often been asked, as researchers who investigated this tragedy, how many other potential landslide disasters exist around the country.

Local seismic measurement stations clearly show that the event happened with no warning and so quickly that victims in its path had little chance to run for safety. Even if it had been slower, there would have been nowhere safe to run — the slide area is almost a mile across.

Early on March 22, 2014, the most damaging landslide in U.S. history devastated the community of Oso, Wash. Forty-three people perished, most inside their homes, when a saturated hillside nearby gave way and a massive mudflow swept over their neighborhood. On July 22, a search crew recovered the last of the 43 bodies, exactly four months after the landslide, and coincidentally on the same day that a team of scientists and engineers released an exhaustive report (read pdf here) detailing the event and its implications.

Radiocarbon dating of landslides near the deadly March 2014 mudslide in Oso, Washington show that this is a geologically active region, with other large slides in the relatively recent past.

Erosion caused by both natural and human activity can cause the soil or rock on a hillside to move downslope or collapse, a process called mass wasting. Over time, gravity acting on such material will eventually cause slow or fast downslope movement. More-rapid movement can constitute a landslide or rockfall; in slower movement, the surface material can creep at rates that may be too slow to see.

William H. Schulz is a research geologist for the U.S. Geological Survey and a member of the Geologic Hazards Team located in Golden, Colorado on the campus of the Colorado School of Mines. Schulz works in the Landslide Hazards Program "conducting research, gathering information, responding to emergencies and disasters, and producing scientific reports and other products for a broad-based user community."

Landslides may occur when water from rain and melting snow sinks through the earth on top of a slope, seeps through cracks and pore spaces in underlying sandstone, and encounters a bed of shale inclined toward the valley.