Geology

Mass Wasting

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Science  10 Sep 2004:
Vol. 305, Issue 5690, pp. 1533
DOI: 10.1126/science.305.5690.1533c

Taiwan consists of an active mountain belt, produced by the collision of the Eurasian and Philippine Sea plates, which forms the spine of the island. The mountains are being eroded by the many landslides caused by earthquakes and typhoons. Taiwan averages about four typhoons per year, and on 25 August 2004, Typhoon Aere produced wind damage, landslides, and flooding on the northeastern coast.

Dadson et al. have measured the changes in sediment concentrations in rivers (normalized to the water discharge rate) for a typhoon (Herb, August 1996), earthquake (moment magnitude 7.6 Chi-Chi, September 1999), typhoon (Toraji, July 2001) sequence. They found that at any given water discharge rate, the sediment load carried by a flood increased by a factor of 4 in the epicentral area: The earthquake, which produced 20,000 landslides, increased the rate of erosion, the amount of sediment delivered to the watershed, and the amount of sediment that is ultimately deposited in marine basins around the coast. Not only do these destructive events provide a natural laboratory to measure rates of erosion directly, but this particular sequence suggests that prehistoric large earthquakes and their rate of recurrence might be decipherable from the offshore sedimentary record. — LR

Geology 32, 733 (2004).

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