Mudslides roared across part of the Trans-Canada highway, near Banff, Alberta. The mudslides narrowly missed several cars and stranded hundreds of travelers. Heavy rains near the B.C. - Alberta border caused the slides.

The mud was one metre deep in some areas of the road, and at its height covered all four lanes of the divided highway.

After many hours of work, clean up crews were able to re-open the parts of the highway.

Parks Canada say it will take several days before all the debris is cleared, and traffic returns to normal.

Mudslides often occur in steep and mountainous areas. They are usually caused by weakened land on hills and mountains. Rivers, glaciers, heavy rainfall, melting snow, earthquakes, or even thunder can weaken the land .

Once a slope is weakened, almost anything can start a mudslide. Rainstorms are a common cause of mudslides. In heavy storms, water soaks into the ground faster than it can run off. Water pressure loosens soil and rocks . When soil and rocks break loose, they become a mass of wet earth that starts a mudslide.

Mudslides can move quickly and powerfully, picking up rocks, trees, houses and cars.

As the debris moves into rivers, bridges can become blocked or even collapse, making a temporary dam that can flood neighbouring areas.

1. What roared across part of the Trans-Canada highway, near Banff, Alberta?