ADVANCES IN THE STUDY OF LANDSLIDES IN THE LAST 50 YEARS IN ENGINEERING GEOLOGY

Landslides are a major geological hazard around the world. In North America they cause 25-50 deaths/year and over $3.5 billion in damage. They are a major hazard for humans because many structures are destroyed each year, but one cannot get normal homeowner’s insurance to cover the damage. The main advances are in the production of landslide maps: inventory maps, susceptibility maps, and risk maps. With the advent of computers and GIS mapping programs, maps can be made quickly and efficiently with accuracy. Combined with modern GPS units in the field the location of landslides can be accurately put onto inventory maps with a lidar base. GIS programs can integrate many factors to produce really good susceptibility maps, and those maps can be overlain by human influence to produce excellent risk maps. All of these maps are now available electronically to the general populace. Second, lidar, a laser imaging system that allows us to accurately map the surface through the trees and recreate that surface with excellent accuracy. Landslide scarps and toes and hummocky topography are so evident without the vegetation. It is not uncommon to remap an area first mapped using air photos to have a 10x increase in number of slides after using lidar. Lidar greatly increases the accuracy of all three types of maps. One can see 3-D without having to use air photo pairs and glasses. In the field, great advances have led to precision of the sizes and shapes of landslides. Laser range finders and total stations give great precision on landslides dimensions. GPS units now give accurate positions. INSAAR satellite images allow us to see slow movement of slides. Portable drilling rigs allow us to sample landslides in the remotest areas. The media has led to increased awareness about landslides so people are asking registered geologists to inspect slopes before building on them. Registration of geologists in 31 states had led to better quality of assessments. Once landslides occur, installation of inclinometers, a fairly new advance, allows us to monitor amounts and depths of movement. Weather forecasting has allowed us to combine susceptibility maps with landslide predictions when thresholds have been determined to give landslide forecasting.