Rainfall-induced lahars on Montserrat
Jan Alexander
(sedimentologist), Adrian
Matthews (meteorologist), Jenni Barclay, Janez
Susnik and Peter Talling (Bristol). In co-operation with the
House at the edge of the Belham River Valley, Montserrat in May 2003 (left) and June 2004 (right) showing the progressive burial of the valley floor by remobilised sediment from the flanks of the SHV, Montserrat.
The remobilisation via rainfall of loose material deposited during the ongoing eruption of the Soufriere Hills Volcano has resulted in profound changes to the geopmorphology of many of the river systems surrounding the volcano. This material has been remobilised via the production of lahars. The term 'lahar' is of Indonesian origin and is used to describe flows involving a mixture of debris and water occurring in volcanic channels. These flows are both directly and indirectly hazardous. They are capable of burying and infilling topography and pre-existing structures as well as being energetically erosive.
We have been monitoring rainfall activity and geomorphological change in the Belham River Valley on Montserrat since January 2001 in order to better understand how these flows behave. With over 3500mm of rainfall and 30 lahar events recorded since the start of the study we have found that the lower reaches of this system are in net aggradation to date. As part of his PhD project (started October 2004) Janez Susnik will be extending this work to other (larger) active systems in the area around Plymouth.
Updated March 2006- Rosie Cullington and Jenni Barclay