Landslides happen everywhere and in different geological locations. This can be because of flooding, which allows sodden soil to move; it can be because of rockfalls, and slower, continuous movements of land due to gravity. Landslides are particularly dangerous when they happen without warning, as recently happened in India and Japan. Tens of thousands were killed in the Vargus disaster in Venezuela in 1999.
Some places are prone to flooding – even, in the case of India, monsoons – but to know where or when a landslide will happen we need good tools. Currently equipment to measure landslides includes rain gauges, such as those used in the Chittagong region of Bangladesh, which record levels of rainfall that can then be compared to previous data of levels that triggered a landslide. But many current systems use point-based sensors: in other words, systems that rely on ground-plugged devices that are able to monitor only from fixed positions.
We’ve been working on a new way of predicting landslides using optical fibres in cables as sensors. The system, called Stimulated Brillouin Scattering, uses the interaction of light with acoustic waves. When installed, it can constantly monitor changes happening to the land; when the soil undergoes collapse or sliding, we can detect the embedded fibre stretching.
These sensing optical fibre cables can be embedded in shallow trenches in the ground, to monitor both large landslides and slow slope movements through the elongation induced in the sensing fibre. If you imagine the land as a body, a distribution of these optical fibre sensors act as the “nerve system”. They have the ability to detect a change of one centimetre over a distance of a kilometre. Being able to measure and track early pre-failure soil movements, it is then possible to detect the signs of an imminent landslide.