11 January 2009

Costa Rica earthquake – landslides have proven to be a major threat

Posted by Dave Petley

News continues to flow in regarding the impact of the earthquake in Costa Rica. It is increasingly evident that landslides have probably been the major problem, which is unsurprising given the topography and soils. The landslides have clearly caused substantial loss of life and are also hampering rescue operations.

The Washington Post is reporting, quite rightly, that there are now concerns about the stability of the slopes in the affected area in the next wet season. The Reuters image below shows seriously deformed ground above the crown of a seismically-triggered landslide at San Rafael de Vara Blanca:

I found the diagram below showing rainfall in San Jose, which is just a few tens of kilometres away:

Fortunately the period January to April is pretty dry, but problems will certainly start in May. Action will be needed to address this as the level of hazard will be high in many areas. At the moment the biggest problems seem to be around the village of Cinchona, on the flank of the volcano, were a family restaurant was buried (see AP images below of Cinchona):

There are certainly lots of other landslides too, as this AP image shows:

Finally, the Washington Post is carrying a slightly intriguing report:

“A wave caused by the earthquake damaged the Cariblanco hydroelectric plant and it will take at least a year to repair, local media quote a senior official as saying.”

A bit of digging shows that AP are reporting that “Officials reported meanwhile that the country’s leading Cariblanco hydroelectric plant will be out of operation for about a year, after its generators were buried by tons of mud from flooding and landslides unleashed by the earthquake.”

According to this site, Cariblanco appears to consist of two 40 MW turbines. It came into operation in 2007 after construction costs of US$170 million. This would appear to be a very expensive set of landslides for such a new project! Unfortunately, our experience elsewhere (e.g. Taiwan) is that sediment delivery increases in the rainy season as further landslides activate, so the operators of this site would be well advised to get some landslide advice.