uncontrolled growth of settlement on hazards hill slopes causing land slides?

Answer 1

Yes, construction on unsuitable sloped surfaces is definitely a cause of land slides. Many geological formations are not stable in the long run. If a careless developer decides to place buildings on such a surface, like a hillside with loose soil, the instability is exacerbated. A slope that would have failed eventually will collapse sooner, sometimes triggered by an event like an earthquake or rainstorm that completely destabilizes the ground.

Answer 2

Human development on unstable slopes is a much larger problem than most people realize. Some HUGE disasters have occured as a result of building structures in the wrong area.

The best example I can think of man-made landslides would be landslides in coastal areas of California. Very expensive properties in places like Malibu are built on top of poorly indurated marine sediment.

By itself the hillside is stable... but once you add a bunch of human development you get problems. For one thing you've got the weight of the buildings, pavement, sidewalks, tennis courts, etc... plus you have many homes with a septic system which is putting water into the ground that lubricates the material. It all adds up to a very unstable slope.

Sometimes this will result in a catastrophic landslide, but usually the effects are much more gradual (called "creep" as opposed to a flow/slide). Materials will move a few centimeters each month, and eventually any buildings on that property will have to be condemned.

A couple other examples of a man-made land slide...

When the Vaiont River in Italy was dammed in the 1960's, the weight of the reservoir water pushed water into the valley walls. This reduced the strength of a clay layer underneath the surface, and resulted in a HUGE rock slide which fell into the reservoir. It sent a wall of water down the river which eventually claimed almost 3000 lives.

In 1903, Turtle Mountain in Frank, Alberta Canada was the site of the largest mass movement in North America in recorded history. The mountain was already geologically unstable, but the mountain was extensively mined for coal (I think it was coal anyway) starting just before the slide occurred. The area of the slide was closely related to the parts of the mountain which were being mined. Dozens of people were killed when 30 million cubic meters of rock fell off the mountain and onto the town of Frank.