The science of big boulders

As outstanding features in the landscape, large boulders have long captured the imagination of humans. But from a scientific perspective they can also provide valuable information on geohazards, such as tsunamis, floods and landslides.

Researchers in the School of Geography, Earth and Environmental Sciences, in collaboration with other national and international research institutes, have been at the forefront of understanding what big boulders can tell us about related geohazards. The novel approaches to boulder studies that we are currently pursuing include:

• automated exploration using space and aerial imagery (including drones) to identify and map, via photogrammetry, spectral signature and shadow, boulders over large, remote or difficult-to-access areas
• innovations in surface exposure (cosmogenic) dating to constrain timing of events
• new developments in using boulder composition to identify the origin and routing of events
• utilising boulder shape and mass characteristics to determine the peak flow volumes of past floods.

Within the School of Geography, Earth and Environmental Sciences at the University of Plymouth, these data are being used to improve our understanding of flood- and landslide related geohazards in vulnerable desert communities in the Western Mediterranean, Saharan region and the Peru-Chile Atacama. In these dry-land settings, occasional extreme floods are often associated with large landslides that amplify meteorological flood size by creating temporary dams, which subsequently breach and fail. In the Peru-Chile Atacama Desert - the oldest and driest desert on Earth - recent (e.g. 2015) floods wreaked havoc on local communities but these events are small in comparison to mega-floods recorded by boulders in pre-historic sediments.

Preliminary research indicates that these ancient flood-boulders originated from > 1 million year old giant-landslide dams, where the landslides are earthquake triggered. The resulting features may lie dormant in the landscape for many years until a meteorological flood event occurs and is impeded by their presence, a factor not accounted for in current hazard assessments in this environment. Unravelling the story of these boulders is currently being undertaken with funding from both National Geographic (Chile) and the Royal Geographical Society (Morocco).