To begin with, landslides, slope movements or mass removal phenomena are the cause of the generation of geological risks that can affect buildings, transportation routes, riverbeds, reservoirs and sometimes can affect entire populations.
Geologists, engineers, and other professionals often rely on unique and slightly different definitions of landslides or mass movements.
This diversity of definitions reflects the complex nature of the many disciplines associated with the study of landslide phenomena.
But basically a landslide is a general term used to describe the downward movement of soil, rock and organic materials under the effects of gravity and also the landform that results from such movement.
The classification or types of landslides are associated with specific failure or slope failure mechanisms and the properties and characteristics of the failure types; these will be briefly discussed here.
There are a number of other phrases/terms that are used interchangeably with the term “landslide” including landslides, slope failure, etc.
What are landslides or slope movements?
With respect to landslides They are mass movements (soils or rocks) that slide over one or several failure surfaces (rupture surfaces). When the resistance to shearing of this surface is exceeded, in sliding the mass moves as a single unit.
Furthermore, in the landslides Large volumes of earth (rocks, soils) (even millions of cubic meters) can be moved at very varied and violent speeds.
The mass movements can be classified into rotational and translational landslides, mud flows (mud), debris or debris flows, overturning and landslides, avalanches, lateral movements and creeps.
Parts of a landslide
Regardless of the exact definition used or the type of landslide under discussion, it is helpful to understand the basic parts of a typical landslide.
The figure below shows the position and the most common terms used to describe the unique parts of a landslide.
- header or crown
- main escarpment
- secondary scarp
- Flank
- cracks
- Foot
- Foot of the rupture surface
- breaking surface
- Upper area
- land mass slipped
Types of landslides or mass movements
| Types of landslides or mass movements | Description |
|---|---|
| Landslides | – Rotational, – Translational in rocks and soils |
| flows | – Mudflows – Debris flows – Rock flows – Creeping – Solifluction |
| Landslides or Falls | Rock and soil slides |
| overturn | – Overturning of rocks – Flexural overturning of rock masses |
| avalanches | – Rock avalanches – Collapses |
| Lateral displacements | Soils and rock blocks |
A landslide is a downward movement of rock or soil, or both, that occurs at the rupture surface, either curved (rotational slide) or flat rupture (translational slide), in which much of the material is often It moves as a coherent or semi-coherent mass with little internal deformation.
It should be noted that in some cases, landslides may also involve other types of movement, either at the onset of failure or later if properties change as the displaced material moves downslope.
This section provides descriptions and illustrations of the various types of landslides.
Understanding the characteristics of the specific type of landslide hazard in your area is vitally important to consider when planning or taking appropriate mitigating measures to reduce the risk of loss and damage.
The type of landslide will determine the potential speed of movement, the probable volume of displacement, the depletion distance, as well as the possible effects of the landslide and the appropriate mitigating measures to consider.
Landslides can be classified into different types based on the type of movement and the type of material involved.
In short, the material in a landslide mass is either rock or soil (or both); the latter is described as dirt if it is composed mainly of sand particles or finer particles, and rubble if it is composed of coarser fragments.
The mass movement type describes the actual internal mechanics of how the landslide mass moves: detachments or falls, slumps, detachments, sliding, overturning, propagation or flow, etc.
Therefore, landslides are described using two terms that refer respectively to material and movement (ie, rockfall, debris flow, etc.).
Landslides can also form a complex fault that encompasses more than one type of movement (rockslides and debris flows).
Rotational slides
With respect to rotational landslides, they are frequent in homogeneous (cohesive) soils, they are characterized by the fact that the failure surface is curved or spoon-shaped, in this landslide the landslide mass accumulates at the foot of the slope as well as a lobe.
Translational landslides
With respect to translational landslides, they can be generated in soils and rocks, failure occurs through one or more failure surfaces (stratification, contact between rocks, planes of weakness) that are flat and oriented in favor of the slope (slope)..
Due to the characteristics of the failure surface, in translational landslides the mass slides faster than in rotational landslides.
Flows
to start the flows either casting They are characterized by being mass movements that involve a high percentage of water in the process, therefore the mass behaves like a fluid that slides along poorly defined failure surfaces.
The main characteristics are: a high percentage of water, they are usually shallow but reach large extensions, the landslide reaches high speeds, even meters per second.
Flow-type landslides are classified into mudflows (mud) either Earth, debris or debris flows Y rock boulder flows.
Mud or soil flows
In the mud flows there is a high percentage of water mixed with clay-type material, for this reason it can be said that they have been generated by the affectation of clayey soils.
Debris or debris flows
In the debris flows there is a high percentage of water mixed with sandy, silty and clayey materials, for this reason it can be said that they have been generated by the affectation of highly weathered rocks.
Rock block flows
In rocky block flows, water has mixed with gravel-sized materials and coarse blocks in a sandy, silty, and clayey matrix, that is, they have affected highly fractured and weathered rock masses.
Reptation and solifluction
The creep It is a very slow and superficial movement of mass, which affects highly altered and weathered soils and rock masses, that is to say, it is practically imperceptible and only measurable with special instruments (constant measurements with GPS).
In addition, creep is characterized by causing continuous creep-like deformation on the surface (deformation over time) and is recognized by overturned trees, misaligned posts, removed walls and fences, etc.
Unlike crawling, solifluction It is a movement that is produced by freezing and thawing, in the most superficial areas of the slopes, therefore this movement is characteristic in cold regions.
Rockslides
Rockfalls occur when pieces of rock from a rock mass fall freely to the surface.
These pieces of rock are produced because the rock mass is highly fractured or affected by discontinuities (joints, faults, bedding surfaces).
Rockfalls are very frequent in steep mountainous areas made up of highly fractured rock masses.
In addition, the blocks that detach can have various sizes, however, being solid with a large volume, they represent a high risk on roads, at the foot of cliffs and in mountainous areas near towns.
Overturning of rocks and soils
The overturning of rocks and soils occur when the rock fronts have vertical strata that are dipping in the opposite direction to the slope.
Rock avalanches
Rock avalanches are formed when there is the collapse of large volumes of rock masses, they are usually associated with the collapse of volcanic calderas.
When this mass movement occurs, it is usually a violent process, which generates the crushing of large blocks of rocks, the result being the formation of a breccia composed of large blocks in a fine matrix of crushed rocks.
Lateral displacements
This type of mass movement is usually regional, originating from the fact that a massive and competent type of rock is found on a soft and deformable material, which allows slow and constant lateral displacements.
Lateral displacements can also be caused by liquefaction of the underlying material, or by processes of lateral extrusion of soft and humid clays, under the weight of the upper masses.