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This is Scientific Americans' 62nd Science. I'm Emily Schwing.

How do you fight an uphill battle when the problem is moving downhill?

That's exactly what Denali National Park's resident geologist, Denny Caps, is trying to figure out.

In recent years, the Pretty Rocks landslide transformed from a minor maintenance concern

to really our foremost challenge. On a crisp fall day in September, just inside the park entrance,

not much is happening inside the offices. Staff here are a week out from buttoning up the park

for winter, but more than 40 miles down the park's only road at a place known as Pretty Rocks.

Things are really moving downhill at up to half an inch an hour.

The Pretty Rocks landslide acts much more like a glacier than it does what most people consider

to be a landslide. Paul Oleg is the director of interpretation and education at Denali.

In that, it is this very ice-rich material that responds to fluctuations in temperature

and will speed up and slow down based on a lot of different factors regarding the level of the ice,

the temperature, the ice, and so we tend to consider the Pretty Rocks landslide to be more like a

rock glacier than what we would typically consider to be a landslide. Oleg says the landslide

is a harbinger of what else may come for the entire U.S. National Park system.

This is in my perspective kind of a canary in the coal mine type of situation where we're on the

...