One of the largest impacts of landslides occurs when the slide severs an oil or gas pipeline, allowing a release into the environment. Given that pipelines are increasingly being built in landslide-prone terrain this is a real problem. A clear illustration of this occurred in Ecuador on 31st May, 2013 when the Trans-Ecuador pipeline ruptured in a landslide.
If you look carefully the broken pipeline is clearly visible, as is the spilled oil. Note that this was not a particularly large landslide. The volume of oil released to the environment is reported to have been about 11,500 barrels, which is about 205,000 litres. The oil flowed into the Coca River and is now making its way downstream.
The initial impact was on the city of Coca, which has 80,000 inhabitants, which had to shut down its drinking water supply. Whilst the volumes of oil do not sound huge, the impacts are enormous. The oil is likely to affect river systems in both Peru and Brazil in due course.
The irony is of course that the cost of identifying and avoiding such likely to be small compared with the costs of losing the pipeline and its oil for a few days, and more importantly with the cost of the environmental damage that this spill will cause.