Landslides or landslips, mudslides, mud slips or mudflows, debris slides or debris slips and rockfalls, while all have some differences from one another, all reference a form of movement of sediment, rock or debris downslope due to gravity. Generally, a landslide/landslip is the general term for a wide variety of processes and landforms involving the downslope movement, under gravity, of masses of soil and rock material.

Landslide along the North Coast Road on September 13th 2017.

Landslide Types

Landslides, the catch-all term for the mass movement of the earth, can be classified into a multitude of categories and types as seen in the matrix below, taken from Wikipedia incorporating several different classifications and definitions over the years.

Schematic landslide classification adopting the classification of Varnes 1978 and taking into account the modifications made by Cruden and Varnes, in 1996. Some integration has been made by using the definitions of Hutchinson (1988) and Hungr et al. 2001.

In Trinidad and Tobago, based on the geology of the bedrock and overlaying sediment, only a few of these types occur on our shores.

Falls (Rockfalls)

Falls are the abrupt movement of masses of geological materials, such as rocks and boulders, that become detached from steep slopes or cliffs (USGS, 2004). In Trinidad and Tobago, rockfalls are common particularly during heavy rainfall, as water dislodges rocks and boulders upslope. Rockfalls can also occur as a result of earthquakes.

Slides (Debris Slides)

Although many types of mass movements are dubbed “landslides,” slides are a specific type of mass movement of sediment. This is where there is a distinct zone of weakness that separates the slide material from a more stable, underlying material.

In a traditional slide or debris slide, there is a chaotic movement of rocks, soil, and debris mixed with water. It is usually triggered by the saturation of thickly vegetated slopes which results in an incoherent mixture of broken timber, smaller vegetation, and other debris. This is common along the Northern Range of Trinidad.

Example of a debris slide along the Lady Young Road on November 17th 2018.

Flows (Debris Flows, Mud Flows, Creep)

Flows are generally more rapid movement of sediment, compared to slides.

A debris flow is the rapid movement of loose soil, rock vegetation, air and water move as a slurry downslope and is typically caused by heavy precipitation. Debris flows typically trigger other types of flows or slides in steep-slope areas, largely consisting of silt and sand-size sediment. This type of landslide occurs mainly in Central and Southern Trinidad but can and does occur along the Northern Range. A debris avalanche is a type of debris flow, but moving at speeds up to and in excess of 160 KM/H.

An example of Debris Flow at Bamboo Village, Cedros, South Trinidad on February 27th 2018.

A mudflow, or commonly referred to a mudslide, is a flow of slope material, i.e. sediment that contains at least 50% fine-grained sediment (sand, silt, and clay-sized particles) that is wet enough to flow rapidly. This type of landslide occurs across both islands, particularly during heavy rainfall.

While a creep falls under a flow, it is imperceptibly slow with a slow, steady, downward movement of slope-forming soil or rock. This type of flow mainly occurs across parts of Southern Trinidad, with the most recent example being the Los Iros landslide resulting from the 21st August 2018 earthquake. The investigation is still ongoing by the UWI Seismic Research Center, but the leading hypothesis by local geologists and geophysicists is that a debris slide was triggered by the August 21st earthquake, causing significant faulting in the area, destroying farmland and severely damaging infrastructure with subsequent creep as sediment continue to move. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridge. (USGS, 2004)

Based on geology, landslides/mudslides in Trinidad can be categorized as debris slides, predominantly in the Northern Range, and mudflows in southern and central parts of Trinidad. A detailed look at Trinidad’s geology and analysis on Landslides in Trinidad can be found in Kanithi & Kanhai (2006).

Landslide Causes

Natural Causes

  • Groundwater pressure acting to destabilize the slope. This is why landslides tend to occur with heavy rainfall in elevated areas, particularly across the Northern Range
  • Loss or absence of vegetation after a wild, bush or forest fire. A lack of vegetation destabilizes the soil, allowing it to move downslope easier.
  • Erosion of the toe (lowest part) of a slope by rivers or ocean waves. This type of erosion and subsequent landslide are most common along Trinidad’s Southwestern, Southeastern and Southern coasts.
  • Earthquakes destabilizing slopes, particularly in areas where slopes may already be unstable due to a combination of natural and human causes.
  • Volcanic Eruptions. While this may not be an issue in Trinidad and Tobago, due to a lack of magmatic volcanos, our neighboring islands do have volcanoes and these landslides may trigger tsunamis, which are of concern to T&T.

Human Causes

  • Deforestation, cultivation, and construction destabilize the already fragile slopes. This is prevalent across the Northern Range, as development continues without proper approval and environmental assessments completed. In shallow soils, the removal of deep-rooted vegetation that binds colluvium (unconsolidated sediments) to bedrock.
  • Vibrations from machinery or traffic or from quarry blasting.
  • Earthwork which alters the shape of a slope, or which imposes new loads on an existing slope. This is the case along the Northern Range, where the North Coast Road has altered the shape of slopes. However, due to geological characteristics, most areas along the North Coast Road and Lady Young Road are in relatively stable areas. However, as seen in recent years, the few unstable slopes have caused chaos when landslides do occur.

Landslide Frequency

Landslides, unlike hurricanes, do not have a season for its occurrence. However, in years that are predominantly wet such as 2017, landslides occur at a higher frequency along the Northern Range. This is likely due to groundwater pressure destabilizing the slope.

Landslide Monitoring & Forecasting

In Trinidad and Tobago, there is no governmental or scientific body that monitors high-risk landslide areas in real time. Even after landslides, only visual monitoring takes place.

Diagram of a typical landslide monitoring setup. (Credit: USGS)

Monitoring may include traditional ground survey techniques repeated over time to determine movement at specific locations. It may include subsurface investigations with the aid of borehole inclinometers and their periodic manual monitoring and even continuous automated monitoring.

Landslide forecasting is the next step after monitoring, as an ample network of sensors and monitoring techniques can give sufficient forewarning ahead of a landslide.

Landslide Effects

  • Loss of life. Communities living in hilly or mountainous areas, particularly across and near semi-stable to unstable slopes of the Northern Range are at a greater risk of injury or death by landslides. Landslides can carry huge rocks, heavy debris, and soil at fast speeds. Persons commuting along roads where slides are possible also run the risk of injury or death by landslides. The highest risk is along the North Coast Road and parts of the Lady Young Road.
  • The Decimation of Infrastructure. The force of the flow of rock, mud, and debris as a result of a landslide can cause significant damage to infrastructure such as roads, property, communication systems, utility poles and lines and in some cases railways. Roads can become impassible, which is usually the case along the North Coast Road.
  • Economic Losses. Beyond the repair cost for infrastructure and property, economic losses can extend to the communities cut off by debris. This is the case in Maracas, as frequent landslides over the last several years have time and time again cut off the Maracas Bay area. Maracas Bay Vendors Association has reported a decline in sales during peak periods resulting from landslides cutting off the area from the rest of the country.
  • Destruction of Landscapes. Erosion left behind after a landslide leaves the landscape barren and unsightly, from what once was likely a green space with vegetation or forest.
Landslide along the North Coast Road, before the Maracas Lookout, on November 26th 2017.
  • Impacts River Ecosystems. Soil, debris and rock from a slide can block watercourses natural flow. This can not only destroy river habitats due to the interference of natural flow of water, but can cause a disastrous flash flood situation if that blockage is removed due to a high volume of water.

Major Landslides

Trinidad and Tobago has experienced several major flood events over the last several decades, with 5 notable disasters between 2017 and 2018.

  • February 2017 Cedros Landslide
  • Maracas Lookout Landslides (2013-Present)
  • October 2018 Lady Young Road Landslide

Landslide Safety

Emergency Numbers

Disaster Management Hotlines & Other Emergency Hotlines for Emergency Services
Disaster Management Hotlines & Other Emergency Hotlines for Emergency Services
Emergency Shelters Across Trinidad

While these buildings are designated as emergency shelters, only particular locations will be opened in the event of a high-impact natural disaster. Keep checking our social media, website, as well as governmental channels for updates on which shelter may be opened near you in the event of a disaster.

Emergency Shelters Across Trinidad. Click for full resolution image from the ODPM

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