When Mount St. Helens erupted on May 18, 1980, the north slope of the volcano collapsed, triggering one of the largest landslides ever recorded. The numbers alone are staggering: 2.8 cubic kilometers of displaced earth and a distance traveled of 22.5 kilometers.
Landslides undoubtedly cause enormous economic losses worldwide. However, predicting their occurrence is very complex because they involve numerous forces and external phenomena. Nevertheless, satellite monitoring and sensor technologies are enabling us to delve deeper into this field. The goal is to provide a better quality of life for residents in landslide-prone areas and help reduce the impacts on linear infrastructure.
How does technology help minimize the impacts of landslides?
Techniques for mitigating the effects of landslides have advanced significantly in recent years. Many of them, such as constructing terraces or retaining walls, are aimed at stabilizing slopes.
But in this article, we will focus on methodologies that, to some extent, facilitate the prediction of these slope movements.
Early warning systems for landslides: Technology for prevention rather than cure
Unlike the structural measures mentioned in the previous paragraph, early warning systems for landslides fall under what is known as “non-structural measures.”
An early warning system can be defined as a “device, system, or set of capabilities that generates and disseminates timely and meaningful information to enable individuals, communities, and organizations threatened by a hazard (in this case, a landslide) to act promptly and appropriately to avoid or reduce the impact of the threat” (1).
These solutions typically include:
- A landslide model that assesses the effects of slope, soil type, or water infiltration on the triggering of an event, supplemented with data captured by monitoring instruments.
- An alert model that establishes the necessary decision procedures for issuing alert levels.
- Mechanisms for dissemination, communication, and education about the alerts.
- Community participation programs.
- Emergency action plans.
These systems are garnering great interest due to advantages such as (2):
- Lower economic and environmental costs compared to structural measures.
- The continuous development of new monitoring technologies.
- The increased availability of reliable databases to calibrate alert models.
Their usefulness has been demonstrated on numerous occasions. An example of this was the Montecito landslide in California in January 2018, where thanks to advance warnings, the majority of the population could be evacuated (although over 20 people still perished).
However, one of the main challenges is implementing these types of solutions in developing countries, where the number of casualties from such phenomena is much higher.
Designing a useful warning system
The landslide hazard has traditionally been estimated using manual techniques, such as visual inspections in the field. However, these methodologies are constrained by factors such as accessibility or resource availability.
The progressive introduction of technology in this field has facilitated evaluation tasks and the creation of increasingly reliable models. Remote monitoring, supported by satellites like the Chinese BeiDou system, is allowing the precise monitoring of landslide-prone areas. This surveillance capacity translates into timely evacuations of population centers and lives saved.
However, these methods are not always accessible due to the costs involved and the level of specific knowledge they require (3). In this regard, the introduction of the Internet of Things (IoT) is enabling a new twist in remote monitoring, opening up the possibility of democratizing its use.
What activities and parameters can be monitored with IoT devices? First and foremost, it is necessary to know which factors can serve as better indicators for early warning. The most common ones are:
- Ground deformation, which is monitored through displacement, velocity, or acoustic emissions. Common devices for its supervision are GPS, inclinometers, or accelerometers.
- Precipitation, where rain gauges or weather stations play a significant role.
- Pore water pressure to monitor groundwater conditions, typically measured through piezometers.
- Soil moisture to determine water content, controlled by dielectric sensors.
Arantec’s experience in landslide monitoring
At Arantec, we have been monitoring environmental variables and phenomena such as snow avalanches for years, in which we are one of the leading companies. In other words, we have the technology and knowledge necessary to undertake these types of tasks.
However, until recently, we had not had the opportunity to participate in a project to assess landslide hazards. This opportunity has come to us through the PyrMove project, part of the Interreg POCTEFA program. This initiative aims to develop and implement tools to reduce and manage the risk associated with landslides in the Pyrenees. With this premise, as you can see in the included images, we have installed a network of soil moisture sensors and an automatic weather station using LoRaWAN and 3G communication technologies.
What are landslides?
It’s possible that, in our enthusiasm to show you everything that IoT technology offered by Arantec can do to improve people’s lives, we started this article from the rooftop. However, the foundations of knowledge on which these technological innovations are based are no less important. So let’s explain why it is necessary to take advantage of all these advances starting from the beginning, by defining what a landslide is.
Types of slope movements
Landslides, in their general sense, are ground movements characterized by the displacement of materials (soil, rock, or organic materials) along a slope due to the force of gravity.
As indicated by the U.S. Geological Survey (4) and González Vallejo (6), several types of landslides can be distinguished:
- Based on the material: rock or soil (or both). The “soil” typology is further classified into “earth” (particles the size of sand or smaller) or “debris” (larger fragments).
- Based on the type of movement:
- Falls, topples, or avalanches, which are associated with vertical or near-vertical slopes. In these cases, materials fall, bounce, or roll, often reaching high speeds.
- Slides, in which rocks or soil move along the slope on one or more well-defined rupture surfaces. They are usually associated with slopes ranging from 35-80%, and the mass tends to behave as a unit with variable speed.
- Flows or mudflows, where water causes soil, debris, or rock blocks to behave like a fluid. They are subjected to continuous deformation and do not show clearly defined rupture surfaces.
- Lateral spread, where rock blocks or masses of soil move over soft material. They usually move laterally at low speeds in areas with gentle slopes.
The following image, taken from the publication “Ingeniería geológica” (6), shows the different types of landslides according to their movement.
Differentiating the typical type of landslide in an area is crucial. After all, thanks to this prior research, specific mitigation measures will be implemented.
Causes of landslides and consequences
In previous paragraphs, some factors such as water that contribute to triggering these geological processes have been mentioned. However, the circumstances that can lead to a landslide are varied.
In general, two distinct causes can be distinguished based on their nature:
- Natural causes, such as water (soil saturation, one of the main triggers), seismic activity, volcanic activity, or erosional processes.
- Human or anthropogenic causes, an important factor capable of altering the conditions and forces acting on slopes. In fact, landslides are considered “the geological hazard most influenced by human activities” (7). Thus, actions such as the construction of infrastructure that destabilizes slopes, changes in natural drainage systems, or deforestation, which weakens the soil, can be the origin of catastrophic landslides.
In addition to these triggering factors, the terrain conditions must also be taken into account. This includes the intrinsic properties of materials and the morphology of the slope.
The consequences of landslides are particularly evident in the socio-economic losses they cause. Linear infrastructure, for example, is one of the elements most affected by landslides. In Spain, this phenomenon represents the second-highest cost, second only to the effects caused by flooding.
However, in mountainous countries with dense and often irregular human settlements, the impact can be dramatic. The following map, reflecting the number of landslide victims between 2004 and 2017, demonstrates the toll that slope movements take in some areas of the planet.
Conclusion
Landslides, slope movements, or mudslides, in their broadest sense, cause enormous economic losses and hundreds of casualties each year, especially in medium- and low-income countries. Predicting their occurrence is challenging. However, the cost reduction of monitoring systems, such as precipitation monitoring (one of the main triggers), facilitates increasing access for more countries to at least a basic early warning system.
At Arantec, we are passionate about technology that helps save lives.
Sources consulted:
- (1) Guzzetti, F., Gariano, S., Peruccacci, S., Brunetti, M., Marchesini, I., Rossi, M., & Melillo, M. (2020). Geographical landslide early warning systems. Earth-Science Reviews, 200, 102973. doi: 10.1016/j.earscirev.2019.102973
- (2) Pecoraro, G., Calvello, M., & Piciullo, L. (2018). Monitoring strategies for local landslide early warning systems. Landslides. doi:10.1007/s10346-018-1068-z
- (3) Butler, M., Angelopoulos, M., & Mahy, D. (2019). Efficient IoT-enabled Landslide Monitoring. 2019 IEEE 5th World Forum on Internet of Things (WF-IoT). doi:10.1109/wf-iot.2019.8767201
- (4) Highland, L.M., Bobrowsky, P. (2008). The landslide handbook—A guide to understanding landslides. Reston, Virginia, U.S. Geological Survey Circular 1325, 129 p.. Disponible en https://pubs.usgs.gov/circ/1325/
- (5) Jiménez, J. (2005) Análisis de la susceptibilidad a los movimientos de ladera mediante un SIG en la cuenca vertiente al embalse de Rules, Granada.Tesis doctoral, Universidad de Granada, Departamento de Ingenieria Civil, Granada. Disponible en http://www.ugr.es/~ren03366/DEA/TEMAS/memoria/DEA_J.Jimenez.pdf
- (6) González de Vallejo, L.I. (coordinador) (2002). Ingeniería geológica. Precinte Hall. Madrid, 744 p.
- (7) Ferrer, M., García, J.C. (2005). Análisis de la vulnerabilidad por movimientos de ladera: Desarrollo de las metodologías para evaluación y cartografía de la vulnerabilidad. Memoria de Proyecto. Disponible en http://info.igme.es/SidPDF/113000/263/113263_0000010.pdf
