Tsunamis: In preparation for the big one
Travellers to Indonesia quickly become aware of its geology. It sits along the most active subduction zone in the world. The constant movement of the Australian plate beneath the Eurasian plate creates volcanos, earthquakes and tsunamis. The trench formed by the plate boundary parallels the coast from Aceh through to the Lesser Sunda Islands; exactly the same stretch of coast targeted by surfers in search of some of the planet's most perfect waves.
Travelling surfers are particularly vulnerable to tsunamis and there are many accounts of their experiences, from Bali in 1977 and G-Land in 1994, to the Boxing Day tsunami of 2004 and the Mentawais in 2010. Many increase the risk by staying at or close to sea level in areas where they may be unfamiliar with the local geography.
The vast majority of surfers are aware of the general danger but may be less aware of more immediate risks. In particular there is increasing concern from geologists about the risk of a magnitude 8 earthquake and accompanying tsunami in the Siberut region. Last month the Jakarta Post reported a series of intensifying earthquakes in the region that caused the Indonesian Geologists Association to express their concerns that a larger quake could be imminent.
9th November, 2015: cluster of seventeen earthquakes within ten hours, just east of the Nicobar Islands. The biggest 6.4, the smallest 4.6. Almost two per hour!
Siberut is located close to the plate boundary at a point below the series of large earthquakes following the huge 2004 quake. Geologists predict that, as each quake occurs, the strain moves down the plate boundary, in this case to a point close to Siberut. Subduction zones produce the largest of all earthquakes and this region has historically experienced earthquakes greater than magnitude 8. So the present concerns are well justified.
Given that the earthquake would occur beneath the ocean a tsunami would be inevitable. The Earth Observatory of Singapore estimate that the tsunami would strike the Mentawai Islands within 5-10 minutes and would be of potentially devastating size. Two previous earthquakes in the region produced tsunamis of different sizes. The 2007 8.4 quake in the southern Mentawais produced a relatively small tsunami, while 2010 7.8 quake produced a large tsunami which killed over 500 people and completely washed away many villages.
NOAA's tsunami travel time map for the 2004 Indian Ocean tsunami
Last year the Indonesian Government ran a disaster relief exercise based on an 8.9 quake with a 10m tsunami but this focused on the Padang region. Surf Aid however have run a three year disaster preparedness program which finished in May 2014 and included the Sipora, Siberut and Nias areas.
While the greatest concern is for local populations the development of numerous surf camps in the area means that more surfers than ever before are at increased risk. If the lead time for a potential tsunami is 5 to 10 minutes it is absolutely essential that camps have a clear well organised plan. This would involve; well marked evacuation routes shown on arrival, mustering points above any likely run up zone, and the provisioning of some kind of shelters with non-perishables and first-aid essentials. In a major event it cannot be assumed assistance will arrive quickly.
The accuracy of any earthquake prediction is always in question. We simply do not know enough to be sure. So the predicted quake may come tomorrow, next week, next month, next year or in a decade. In this case though the recent history of quakes progressing down the fault is ominous. If you are planning a trip to the region it is well worth asking your travel agent, land camp or boat captain about their preparedness. Oh and make a donation to Surf Aid. If it doesn't save your life it will almost certainly save someone else's! //blindboy
You can donate to SurfAid here.