23 April 2010

On morbidity and mortality in landslide disasters

Posted by Dave Petley


Landslides kill thousands of people each year across the world but, strangely, there are very few studies of the causes of the injuries and deaths that people suffer when they are affected by a landslide. This contrasts with avalanches, which has a long track publication history of causes of mortality.  This is important in the context of treatment of victims – in particular, where a rescue is ongoing, the medical practitioners need to be able to prepare for the likely state of those who might be recovered.

In this context, a fascinating article, Sanchez et al. (2009), was published in the journal Disasters late last year in which a group of medical and well-being experts examined the causes of morbidity and mortality associated with a landslide disaster that occurred in Micronesia in 2002.  The event was a series of rainfall induced debris flows that occurred on the islands of Chuuk on 2nd July 2002 as a result of the passage of a tropical storm named Chata’an.  The storm reportedly triggered 265 landslides, 12 of which caused a total of 43 deaths and 48 injuries that required hospital treatment.  There is an nice pdf of a presentation by Herman Semes Jr on the background to this disaster here, from which the following images are taken:

The research team interviewed 52 survivors of the disaster, plus a number of eye-witnesses and also reviewed the death certificates of those who lost their lives.  The landslides themselves were slumps that transitioned into debris flows, the largest of which had a volume of 1.5 million cubic metres.

There are some really interesting results of the study, which I will summarise below:

Cause of death
Even though the slides were rapid debris flows, 39 out of the 43 deaths occurred through asphyxiation, with only four resulting from trauma.  Even for those who died outside of buildings, the majority of deaths occurred through asphyxiation.

Types of injuries
For those 31 victims who were injured by the landslides and required hospital treatment, and for whom information on their injuries was available, 16 suffered lacerations, nine contusions/abrasions, four concussions and only two fractures.

Gender of victims
About 58% of those killed by landslides were female, even though women represent 39% of the general population. 

The age of victims
The fatalities were recorded on individuals aged between two months and 84 years, with a median age of 14 years old.  The comparison group of survivors had a median age of 29 years, suggesting that landslides preferentially killed the young. 

Location of victims
Very surprisingly, the study found that “being inside a house or building during the landslide was associated with a higher risk of mortality”, although the difference in risk is not statistically significant.

This study is really interesting – we desperately need more research of this type!  The observation that most of the fatalities occurred as a result of asphyxiation is consistent with avalanche research, but given the greater potential for the materials in landslides to cause trauma, it is a slightly surprising observation.  It is also notable that the landslides appear to have preferentially killed the young – probably a reflection of ability to escape an oncoming event.  Finally, the observation that structures offered no obvious protection is also interesting, but may reflect both the poor quality of buildings in a less developed country, and the fact that a structure may prevent an individual from seeing / hearing an approaching landslide, and may inhibit escape once it occurs.

Sanchez C, Lee TS, Young S, Batts D, Benjamin J, & Malilay J (2009). Risk factors for mortality during the 2002 landslides in Chuuk, Federated States of Micronesia. Disasters, 33 (4), 705-20 PMID: 19459918