It has been said that scientists in a third world country should focus on solving the most pressing problems of the society. Spending taxpayers' money on fancy research is not only a waste but is a moral transgression.
If such is the case, why a few papers on landslide in a country that is most prone to it? It is in the Philippines that two of the most devastating landslides have occured in recent history. One involved a natural formation, a mountain in Southern Leyte, in 2006, and the other involved mountains of garbage in Payatas in 2000.
In an attempt to fill in the void, researchers from the Instrumentation Physics Laboratory of the National Institute of Physics devised a small-scale experimental analog of large-scale avalanches, and, together with a discrete mathematical model, presented their results in a paper accepted for publication in Geophysical Research Letters, published by the American Geophysics Union and considered to be the top journal for geophysics [1].
Table top?
The experimental setup consists of a sand mound perturbed simultaneously by shaking and water pouring. As simple as it is, the analogy presented - sand as the mountain, shaking as tectonic activity and water pouring as rain - has profound implications in the study of landslide hazards.
For one, the earth is tossing and turning in the solar system at the rate of hundreds of kilometers per hour. How do you check if small, almost static sand piles can really capture the dynamics of the majestic land formations in the very mobile planet?
The answer, it seems, lies in the STATISTICAL SIGNATURES - the landslide frequency-size distributions, and the inter-event time series (i.e. the distribution of the waiting times between events of a given thresholds).
Landslide hazards have been classified as self-organized critical (SOC) phenomena, and the first model used to introduce SOC is the sandpile model by Bak, Tang and Weisenfeld [2]. The sandpile is essentially a "landslide" dynamics, albeit at a small scale. It describes how a very small perturbation, even a single grain of sand, can cause avalanches several orders of magnitude bigger than its own size when poured into a critical system.
Empirical data of landslide occurrences in history have been well documented, landslide-prone areas can now be assessed, but models of landslides can be of further help in understanding the underlying mechanisms causing these extreme events. Small-scale setups have the advantage of capturing landslide characteristics, without actually burrying a town.
Cellular automata model
Modifications were introduced to the existing continuous sandpile model to complement the small-scale experiment results.
Intuitively, mountain slopes decay in steepness after avalanche events. This is incorporated in the cellular automata (CA) model in the form of a decaying rule for the stress passing fractions to nearest sites.
CA and small-scale experiments show good correspondence in spatial and temporal signatures.
Signatures which are typical of landslide systems.
"Frustrating" first
The paper, as accepted, has gone a very long way as compared with the originally submitted manuscript, thanks to the tedious review process by no other than the expert in extreme events, Dr. Bruce D. Malamud.
The original paper included "sloppy" mistakes in presentation, and Malamud admitted that the paper is "frustrating to review", but something interesting may possibly come out of it and he encouraged revision. He even disclosed his identity in the middle of the review process and offered many suggestions for improvement.
"After four rounds (yes, four rounds not including 2-3 personal correspondence with the reviewers!) of extensive reviews," Anthony, one of the authors, wrote in his blog [3], the paper was "finally...Officially Accepted: August 22, 2008."
The paper is the first work by a Philippine-based laboratory to be accepted in GRL.
- Juanico, D.E., Longjas, A., Batac, R., and Monterola, C. (2008). Avalanche statistics of driven granular slides in miniature mound, Geophys. Res. Lett., doi:10.1029/2008GL035567. [pdf]
- Bak, P., Tang, C. and Weisenfeld, K. (1988). Self-organized criticality. Phys. Rev. A 38, 364-374.
- http://anthonytons.multiply.com/journal/item/23/My_First_International_ISI_Publication
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