Widespread landslides in Rio de Janeiro and Niteroi in Brazil

Over the last few days the city of Rio de Janeiro, and its twin city Niteroi just across the water, have been affected by extremely intense rainfall - a reported 288 mm in 24 hours.  The upshot has been a series of flash floods and landslides that have killed over 100 people so far.  More heavy rain is expected today.

O Globo has produced an interactive map of the Rio and Niteroi regions in which readers are invited to add information about their area.  This gives a first order estimate of the impacts of the rainfall:

Alagamento = flooding;
Lixo, lama e avores = garbage, mud and trees
Deslizamento = landslide
Postos de deocoes = Donation stations

It appears that many of the slides have affected the shanty towns constructed on the hillsides around the cities.  Over the next few days I will try to collate a list of the major fatality inducing landslides, but for now
O Globo has these two images of landslides that have affected residential areas:

Strangely, it is often a slightly abstract image that captures the horror of the event.  O Globo also has this exceptionally powerful photograph:

Finally, it is interesting to note that this rainfall event appears not to have been captured by the TRMM landslide warning system:

24 hours of rainfall (the yellow circles indicate those areas considered to be at risk of landslides):

72 hours of rainfall (the yellow circles indicate those areas considered to be at risk of landslides):

More later.

New atlas of natural disaster threats in the Andes

On Friday the Andean Community of Nations (CAN) (Bolivia, Colombia, Ecuador and Peru) released an atlas of potential natural disasters affecting the countries of that region, which has come out of the PREDECAN project. It presents maps of the distributions of earthquakes, volcanic eruptions, landslides, flooding, frost and drought, with a special emphasis on El Nino / La Nina.

As far as I can tell this atlas is available only in Spanish (not unreasonably of course), but it is available online in its entirety, which is certainly one better than the World Bank hotspots project. Of course I am most interested in the landslides section - and this deserves more than a single post - but for now let me just give an overview of the landslides chapter.

The headline figures in the analysis are that between 1970 and 2007 about 11,000 people were killed and 38,000 homes were destroyed by landslides. About 260 landslides killed more than 20 people and/or destroyed more than 50 houses. El Nino is a key control on the occurrence of slides. The following map presents the distribution of fatal landslides, with the size of the spot representing the number of fatalities in each case. The darker grey area is the zone covered by this study:

The study also presents the results of an analysis of trends of occurrence of larger (20+deaths and/or 50+ homes destroyed) landslide accidents:

Clearly the data suggest that more landslides have occurred since the mid 1980's than before, but this may well be an artifact of the data. Note that since the mid 1990's there is no clear overall trend, although the period in the late 1990s characterised by the large El Nino event is clearly evident in the data. A moderate El Nino event is thought to be developing at present.

Updated: Large landslide in Peru

Various Peruvian news agencies, such as Adonde.com, are carrying reports of a large rainfall-triggered landslide on Saturday night / Sunday morning in Peru. This slide, which appears to have occurred in the town of Retamas in Parcoy District of Pataz Province, has reportedly buried a number of houses, killing 13 people. The following perspective Google Earth image of the location suggests that landslides may well be a substantial problem in this area (the location is -8.0197, -77.4783 if you want to take a look for yourself):


Helpfully, the following image of Retamas is available on Panaramio at this page:


I guess it is not hard to understand how a landslide can kill 13 people in this landscape. As an aside, given that this is an area of high seismic hazard, those ridge line dwellings look very poorly located.

Update: the Latin American Herald Tribune has an article with further information here. The aricle also has an image:


The slide appears to have occurred on a steep slope above the town. The article notes that the town is “is situated on the side of a mountain and whose residents mine gold and silver...The informal mining operations in the town have affected the stability of the soil in the area", which explains the large scarps on the Google Earth image.

38 years ago today - the Chungar landslide in Peru

Today is the 38th anniversary of a notable landslide - the Chungar rock avalanche in Peru. This landslide occurred on the banks of Lake Yanahuani (sometime spelt Lake Yanahuin), about 120 km north-east of Lima (see image below):

The landslide, which had a volume of about 100,000 cubic metres, is shown on the image below. Unfortunately the Google Earth image resolution is low in this area, but you can see enough to get an idea. I have annotated the image to show the main features (click on the image for a better view):
The rockslide descended a vertical distance of about 400 m before entering the lake, whereupon it created a displacement wave that crossed the body of water at high speed. The wave struck a mining camp located on the other side of the lake, running up a vertical distance of 30 m and erasing all traces of the settlement. Between 400 and 600 people were killed. The landslide occurred on highly-fractured limestone rocks on a slope that had been over-steepened. The slope remains highly dangerous. Unfortunately the landslide is poorly documented - for example, the trigger is really not at all clear.

Landslide buries a gold mining village in Peru

Reuters is reporting that at least 10 people have been killed and a further 30 are missing after a landslide struck the gold mining village of Huanchumay, which is situated in a remote part of Carabaya province. They quote a civil defence official, Victor Ibanez, as having said:

"We have 10 dead so far and five wounded. We have no accurate data for the missing but are talking about 30 to 35 missing people. The landslide took place early on Monday morning and was due to heavy rain in the area.'

The image below shows the general location of the mine in Ayapata. This is pretty inhospitable terrain.

Earthquakes, landslide disasters and the collapse of civilisations

There is a very interesting paper being published next week in the Proceedings of the National Academy of Sciences by Dan Sandweiss, Ruth Shady, Mike Moseley, Dave Keefer and Charles Ortloff. This paper, which is reported in a long press release from the University of Florida, combines archaeology, geology and geomorphology to look at the collapse of the Supe civilisation in Peru, which survived for a couple of millennia in the coastal areas of North Peru before it appears to have abruptly collapsed and disappeared about 2000 years ago. The civilisation is intriguing because they built large and complex pyramids, some over 30 m high, as shown in the Google Earth image below. To be able to build such structures the society must have been complex and organised, so why did it disappear so abruptly?


The paper suggests that about 3,600 years ago the area was struck by a massive earthquake, an idea that is not unreasonable given that we know that this a highly seismically active area. The earthquake caused widespread destruction to the towns, but given the length of time that the civilisation survived in a seismically-active area, this would not have been the first time that this happened in all probability. The key factor was the triggering by the earthquake of massive landslides on the adjacent hills, which moved large amounts of debris into the valleys (as happened in the Wenchuan earthquake last year). This debris was then mobilised by floods triggered by heavy rainfall (again, as happened recently in Sichuan), probably associated with strong El Nino events, which bring heavy rain to this part of the world. This mobile debris would have been a hazard in itself, but more importantly it washed out to sea, whereupon it was redeposited on the coast to form a feature called the Medio Mundo, which is a large coastal bar (see below - click for a better image in a new window):

The Medio Mundo sealed off coastal bays, and thus eliminated a major source of food. Furthermore, sand from the ridge blew inland on the prevailing winds, swamping farms and communities. The huge resultant sand deposits, with the wind sculpted features, can be seen on the image above. Within a few generations the civilisation collapsed, never to recover in that form.

All-in-all a very interesting story that shows how combinations of events can lead to catastrophes. There are lessons to be learnt by modern societies from this!

Colombia landslide images

On Sunday a landslide occurred in the El Polbado neighborhood of the city of Medellin in Colombia. It is believed that 12 people were killed. ArabianBusiness.com has published the following images of the aftermath of the event:



It is clear that this happened in a fairly wealthy area of the town, unlike many landslides in S and C. America, which occur in the slums and garbage dumps. Steep slopes are so often occupied by the very poor (as they cannot afford land on the plains) and the very rich (who like the views and the cleaner air, plus maybe a sense of superiority.