Landslides
Landslide is the movement of material down a hillside, slope or cliff, under the influence of gravity. Landslides are generally controlled by slop morphology, sedimentary — rock lithology patterns, and groundwater regime. There are different types of landslides: large (up to 20-30 sq. km) and small, fast and slow, active, inactive, and relict.
There also geohazards of other types caused by downslope movement of material — rock falls, block toppling, debris flows and mud flows, and others. Debris avalanches and debris flows are not particularly look like landslides, but media reporters erroneously often call them landslides. Earth flows are very similar to translational landslides. Earth flow is the collapse of a wet, steep slope in a series of steps, above the clay or bedrock surface.
There are specific morphological features that can distinguish landslides from other mass movement phenomena. The three major types of landslides are:
- rotational slides in which the surface of rupture is curved concavely upward and the moving mass slides along this concave surface; at their heads a crescent shaped scarp or crown; at their slumps (toes), material can flow slowly downwards; the moving mass consists of thick, uniform material
- translational slides take place when the moving mass slides along semi-planar surface; the moving mass can consist of a coherent mass of regolith or bedrock;
- block slides are translational slumps in which the detached landmass consists of a single block or a few related blocks of little- or non-deformed material.
Mass movements often pose a complex and costly problems for engineers, due to the difficulty of distinguishing their mechanism and prediction of their dynamics. Landslides alone cause tens of millions of dollars in damage and claim tens of lives, mainly in developing countries.
How we can help?
Zesmill provides the complete range of service to engineering and geomorphology mapping, landslide inventory, slope-stability and landslide risk assessments, coastal and river banks hazard definition studies.
Zesmill provides:
- desk-based and field geological studies including field mapping, drilling, stratigraphic and lithologic analysis, neotectonic analysis, etc.
- desk-based and field geomorphological studies
- aerial and satellite image interpretation including multi-spectral, and historical images, LIDAR images, for evaluating the mass movement and landform detection
- SAR interferometry (InSAR) with L, C, X bands data, multi-temporal InSAR measurements
- digital photogrammetric techniques, DEMs comparison for measuring horizontal surficial movements of landslides and earth flows
- RTK GPS and total station surveying to monitor landslide displacement
- hydrological and hydrogeological studies
- 2D and 3D electrical resistivity tomography, microgravity, self or spontaneous potential prospecting, and other geophysical surveys
- detail landslide mapping at a scale of 1:500-1:5000
- mapping of landslide prone areas and landslide inventory
We specialize in large projects — like landslide mapping and inventory — where all these methods can be can be used comprehensively.
Zesmill collaborates with companies and academic institutions that provide site-specific geophysical, geological, and geotechnical studies. Please note that we are not civil engineering company and do not deliver geotechnical analysis, slope stability calculations or structural measurements.
Assessment of landslide prone terrains
Landslides often occur at specific locations under certain topographic and geologic conditions. Therefore it is important to collect comprehensive new information and utilize archive data to understand the topography, geology, groundwater regime and dynamic of active and inactive landslides. Many deformations can result from reactivation of pre-existing (“ancient”) landslides after earth moving works, seismic impact, during above-normal (in moderate climate—warm) precipitation years.
To study landslide processes we usually apply the combination of terrain analysis, geological-geomorphological and geophysics methods.
Zesmill’s specialists performed projects for landslide assessment, monitoring, and inventory projects in Ardennes, Belgium; Altdorf, Germany; Ternopilska oblast, Ukraine; and Osh region, Kyrgyzstan.
Active landslide monitoring
At Zesmill, we use various methods to monitor the active landslides: digital photogrammetric techniques, satellite InSAR interferometry and surveying with total stations, GPS receivers, and terrestrial laser scanners.
If aerial or ground (TLS) photogrammetric methods are used, it is important to pick precise ground control points on the land slump surface, and surrounding stable areas to tie old and recent images together and calculate the displacement of slope surface. All surveying methods are even more labor intensive and require the local geodetic network to be installed. Meantime they provide the most accurate results surpassing SAR-based techniques and automatic measurement devices.
Landslides rarely move uniformly and evenly, so repeated monitoring during five, ten, or even twenty years is the most reasonable decision, as well as using inclinometers, jointmeters, piezometers, and other devices for permanent geomonitoring.
Landslide inventory and cadastre
The main purpose of landslide inventory is to map active and past landslides, to detect their types and major triggering events, and to create landslide maps and databases at national or regional scale. The major categories are common to all databases or cadastres are: landslide location, size, activity, movement type and mechanism, slope shape and angle, geomorphic position, confining beds, and damage done. Additional information may include triggering cause, lithology, stratigraphy, and structural setting, remedial measures etc.
GIS and GIS-database applications allow for effective store, sharing and disseminating of landslide inventory information and maps. Inventory maps depict all registered landslides as well as main geomorphologic regions, aquifers and springs, tectonic faults, and landslide susceptibility zoning.