OSO — Eight months after a landslide tore into this unsuspecting community, researchers have a fairly good idea what caused the hill to fail in such a spectacular and deadly manner.

The slope has been susceptible to landslides for centuries, and an extraordinary amount of rain last spring prompted the latest event. This time, 43 people in its path were killed.

A new episode of the PBS science show “Nova” explores what is known about the Oso slide and seeks to explain what caused the fast-moving slurry of liquid. It also shows how such catastrophes might be predicted so that people can be warned and evacuated. The program airs Wednesday at 9 p.m. on KCTS-TV.

Made by Bainbridge Island filmmaker Liesl Clark, “Killer Landslides” balances the emotional stories of first responders and survivors with a state-of-the-science look at what likely happened at Oso on March 22.

While much of the material will not be new to Snohomish County viewers, “Killer Landslides” is essential watching for anyone wanting to understand the science of landslides. That science is framed by dramatic storytelling and imagery.

Clark used interviews with survivors, including Amanda Skorjanc and Robin Youngblood, to dramatize the overwhelming scale of the slide and cost in lives and livelihoods. The interviews are accompanied by footage of emergency operations.

On the science side, University of Washington geomorphologist David Montgomery and U.S. Geological Survey hydrologist Richard Iverson play prominent roles. Montgomery serves as a tour guide of the slide zone, walking the headscarp and poking through the soil and describing its characteristics. Iverson demonstrates how analyzing the debris flow enabled rescuers to more easily find victims in the mud.

The film avoids issues of governmental policy and liability that have sprung up in the aftermath. “Killer Landslides” doesn’t speculate, as some have, that logging might have been a proximate cause, or that planners in the 1950s shouldn’t have issued development permits for the neighborhood that was destroyed 60 years later.

“Killer Landslides” takes material that is familiar and crafts a new narrative that takes the viewer on an emotional and intellectual journey.

And some material hasn’t been seen before, including Iverson’s experiments at the USGS’s landslide-modeling flume in Oregon.

The episode also visits landslides in Afghanistan, where a slide killed at least 400 people in May; Nepal, where the monsoon season frequently causes slides that block mountain roads; and Switzerland, where researchers have developed a new technology called interferometric synthetic aperture radar to measure earth movement from afar to accurately predict a large landslide, allowing people to be evacuated in time.

Chris Winters: 425-374-4165; cwinters@heraldnet.com. Twitter: @Chris_At_Herald.

‘Killer Landslides’

The “Nova” episode airs at 9 p.m. Wednesday on KCTS-TV and will be followed by a rebroadcast of KCTS’s “In Close: Voices of the Oso Landslide” at 10 p.m.