The bounty - and threat - of volcanic sand

 
"The people of Merapi see the eruptions as part of the natural cycle of life and a reminder of mankind’s insignificance in the face of the forces of nature. After each eruption, which many others see as a calamity, the soil becomes more fertile; for the locals, Merapi is simply cleansing itself of the greed and immorality of the people. For those whose lives are spared, they are rewarded with an abundance of high-quality crops and volcanic sand that they can sell for a good price."

Mount Merapi, just thirty kilometres from the old and wonderful city of Yogyakarta in central Java, is one of the world’s most active volcanoes. It makes its presence known every ten years or so, with clouds of ash, lava, and, most devastatingly, pyroclastic flows. These are dense clouds of superheated gas and rock fragments that roar down the mountain at speeds that engulf and destroy everything in their path – it was such an event that so famously destroyed Pompeii and Herculaneum. And then there are the lahars, a term appropriately of Javanese origin, mudflows, debris flows of boulders, sand, silt, and clay that hurtle down the valleys. The rock fragments carried by pyroclastic flows and lahars are dominantly sand-sized, and Merapi is mantled in these deposits, its rivers working constantly to unburden themselves of this load. For the people who live high on the mountain’s slopes, many in villages only a few kilometres from the crater, the mountain is both a threat and a provider of bounty. The soils are refreshed and re-fertilised, and the sand is an economic resource – its character and chemistry make it ideal for construction purposes and sometimes of a quality usable in water filters. And so sand mining underpins the economy of these villages high on the volcano. A truckload of this sand can bring more than $150 and a worker can earn $3 a day (that's good).

After the recent period of eruptions, the Government is endeavouring to expand the designated park areas on the upper slopes and move the inhabitants to newly-constructed designated communities in safer areas. But such attempts have met with failure before and likely will again. For the locals are not only hardy, and determined to cling to their sources of livelihood, but they are also devoted to the volcano that is their home – as an article in Monday’s Jakarta Globe (from which the quotation above was taken) describes, “The locals consider the mountain their ancestor, whose might and devastating power should be respected.” The people who live on Mount Merapi display that fascinating amalgam of Islam and ancient animism that is common in Indonesia. One of the fatalities in the recent eruptions was Mas Penewu Surakso Hargo, or Mbah (Grandfather) Maridjan, gatekeeper of the mountain, appointed to mediate with its spirits - “My job is to stop lava from flowing down. Let the volcano breathe, but not cough.” His body was found in a position of prayer – he had completed his duties as spiritual mediator with the mountain.

The reworking and redistribution of the debris of recent eruptions by gravity and the mountain’s rivers continues on a vast scale long after the volcanic activity has ceased. In today’s Jakarta Globe, an article headlined “No End in Sight for Merapi’s Mud” describes the continuing threat to villages posed by the surging, sediment-laden, waters: the erosive power of these flows, travelling at 50 meters a second, is staggering. And far-reaching – the city of Yogyakarta, together with surrounding infrastructure and agriculture have suffered extensive damage. The article describes how “the lahar carried by the rivers has damaged or destroyed 1,000 homes in March alone.” It describes how last autumn’s eruptions “dumped 150 million cubic meters of ash and rock onto Merapi’s slopes. It is estimated that two-thirds of that remains on the mountain.”

So sand mining actually helps – albeit on a small scale – to clear Merapi of its geo-rubbish, not to mention maintaining the livelihoods of people whose villages may have been devastated by their ancestor.

[For a fascinating analysis of Merapi’s sediment budget and ways of potentially constructively managing sand mining in that context, see http://www.dpri.kyoto-u.ac.jp/nenpo/no52/ronbunB/a52b0p65.pdf; images from http://javasugar.wordpress.com/page/2/ and http://www.free-world-news.net/2011/01/08/4-trucks-trapped-and-buried-by-volcanic-material-merapi-lava-floods/]

 

Comments

[Melinda]

Hi,
I found your blog through a link from my own blog, Java Sugar, and to my surprise found that you had used my photo of Mount Merapi (thanks for the attribution). I read what you wrote about that uppity volcano and appreciate your research and insight.
Melinda

[Sandglass]

Hi Melinda - many thanks for your comment, and for the great photograph. I'm very conscious of attributions and I hope that this was sufficient - please let me know if you would like anything added.

I look forward to exploring your blog further.

Best

Michael