Technology brings new knowledge about rockfalls

Technological development and advances in remote sensing have brought new data about rockfall incidents.

A rockfall occurs when small to large rock fragments detach from slopes and fall downslope. They constitute a hazardous type of landslide that may result in severe infrastructure damage or even casualties. Therefore, understanding and quantifying these incidents are of high scientific importance.

Researchers are currently capable of thoroughly studying rockfalls. New technological features, including remote sensing and computing power, have enabled better monitoring of a slope to detect successive rockfall incidents. 

Until recently, scientists would monitor a slope to detect new rockfalls once every month in the best case. Unfortunately, this time period between two consecutive evaluations leads to less accurate results. In theory, the number of large rockfalls is overestimated while the small rockfall incidents are underestimated (due to the fact that small incidents may be misinterpreted as a large one). 

According to a new study, recently published in the Journal of Geophysical Research: Earth Surface, the monitoring interval (the time period between two consecutive data measurements) significantly alters the knowledge on rockfalls.

"A primary challenge occurs when neighboring events within a single monitoring interval are recorded as one, producing ambiguity in event location, timing, volume, and frequency. Identifying measurement intervals that minimize these uncertainties is therefore essential," the study states.

Scientists focused on a cliff located in the town of Whitby, UK. The cliff that consists of sandstones, shales and mudstones, is prone to rockfalls due to coastal erosion. Small rockfall incidents are more common than large ones. The research team consistently collected data for 10 months using terrestrial lidar and derived the changes of the cliff caused by rockfalls.

The findings of the survey show that altering the monitoring interval highly affects the number and the volume measurements of rockfalls. In particular, when monitoring was conducted on an hourly rate, 61 rockfall incidents per day were recorded. On the contrary, only 6 rockfalls per day were assumed when monthly investigations were carried out. 

Scientists mention that the rates increased for intervals shorter than 12 hours whereas for those larger than 12 hours, the rates were practically the same.

Authors suggest that the observed increase in rockfall rate has a crucial impact that should be incorporated in hazard prediction models.