Seismic GLOFs and an ecological flood warning system

A Science article (Cook et al., 2018) reports the first seismic recordings of a glacial lake outburst flood (GLOF), a flood caused by the sudden drainage of either a moraine or glacier dammed lake. The flood occurred in the Bhotekoshi River (Himalayas). Kristen Cook and her research team demonstrate how seismometers and geophones placed along the valley picked up two distinct pulses of high-amplitude noise. The first pulse, travelling at 8.7 m/s between recording stations, was the water wave. This was followed by a higher magnitude, but slower pulse (5.0 m/s), interpreted as boulders carried by the flood. The boulders produce a higher frequency sound range (20-80 Hz) than water (2-5 Hz) hence the two can be distinguished. The authors use their data to argue the amount of erosion caused by GLOF events is greater than during monsoon floods.

 

Baker RiverA remote reach of the Río Baker near Corte San Carlos – GLOFs have passed through here since the end of the last ice age.

The article reminds me of a landscape story heard on fieldwork in Chilean Patagonia. As part of our research investigating GLOFs at the end of the last ice age (Thorndycraft et al., forthcoming) we were walking down the Río Baker, to the Corte San Carlos. We stopped at the last house on the track to chat to local farmers. Sitting round the wood burning stove, handing round the mate pipe, they told us about floods in the Baker valley. Nowadays there is a GLOF flood warning system in place – when lake waters in the upstream glacier-dammed Lago Cachet II suddenly drop an alarm is triggered. The warning is passed down the valley by radio. But before such technology existed, the early warning system was the insects living in the floodplain meadows. An onrushing GLOF triggered vibrations down the valley, into the floodplain and up through the grasses. A mass of insects rising out of the meadows was the sign to move livestock to higher ground and safety. An ecological flood warning system.

DSCF7995Corte San Carlos was cut into this cliff face in 1901 to provide access from inland pastures to the navigable lower Río Baker and the Pacific. 

 

 

Footnotes

Kristen L. Cook, Christoff Andermann, Florent Gimbert, Basanta Raj Adhikari and Niels Hovius (2018). Glacial lake outburst floods as drivers of fluvial erosion in the Himalaya. Science 362, 53-57.

Varyl R. Thorndycraft, Jacob M. Bendle, Gerardo Benito, Bethan J. Davies, Carlos Sancho, Adrian P. Palmer, Derek Fabel, Alicia Medialdea and Julian R.V. Martin (forthcoming). Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonian Ice Sheet. Quaternary Science Reviews.

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