This Earthcache brings you to a part of Fort Canning Park that now bears the mark of Mass Wasting. On 4 January 2021, after prolonged monsoon rains, due to mass movement, a Burmese Banyan Tree (a large Heritage Tree) collapsed and fell down the slope, causing some infrastructural damage, but fortunately, no loss of life. This Earthcache serves to use the scars of this incident to highlight to causes and types of Mass Wasting that frequently occur.
Section 1: Earthcache Tasks
At the posted coordinates, you will be looking at the site that exhibits evidence of mass wasting due to heavy monsoon rains in January 2021.
Based on your observations of the Mass Wasting on site, answer the following questions:
- What factor(s) do you think led to the Mass Wasting here? What evidence do you see on site that supports your answer?
- What type of Mass Wasting do you think occurred here? Explain your choice based on your observations and the information provided in the listing.
- What measures have been taken to ensure slope stability in the present day?
And to prove that you visited the site:
- Take a photo of yourself or a personal item with any of the nearby directional signs for the park. Please do not post any photos of the site of the Mass Wasting itself in your log.
As with all Earthcaches, please send your responses to me via email or the Message Centre. There is no need to get all the answers perfectly right as long as a conscious and honest effort is made.
Section 2: The Phenomenon of Mass Wasting
Mass wasting, also known as slope failure or mass movement, is a geological phenomenon where large quantities of rock, soil, or debris move downslope under the influence of gravity. It occurs when the forces holding the material in place are overcome, leading to the movement of the material downhill. Let's delve into the causes and different types of mass wasting.
Causes of Mass Wasting
Steep Slopes: Slopes with a steep angle are more susceptible to mass wasting because gravity has a stronger pull on the material. The steeper the slope, the greater the force pulling the material downward.
Weakened Materials: Materials that make up slopes, such as rocks, soil, or debris, can become weak and lose their ability to resist gravity. This can occur due to weathering, which breaks down rocks over time, or other factors like freeze-thaw cycles, chemical reactions, or biological activity.
Water Content: The presence of excess water can significantly affect the stability of slopes. It adds weight to the material, increasing the downward force and reducing the strength of the materials. Water can infiltrate the soil, saturating it and making it more prone to sliding or flowing. It can also act as a lubricant, reducing friction and facilitating movement.
Earthquakes or Vibrations: Sudden ground shaking from earthquakes or human activities like construction can disrupt the stability of slopes. Earthquakes generate intense vibrations that can weaken the materials, causing them to lose their cohesion and triggering mass wasting events.
Types of Mass Wasting
Mass wasting comes in a few forms, characterized by what moves (rocks, mud and/or debris) and how it moves. These are the main categories:
Debris Flow: Debris flows involve the rapid movement of water-saturated debris down a slope. They are commonly triggered by heavy rainfall, snowmelt, or the failure of a slope holding a large amount of loose material. Debris flows have a mixture of water, mud, rocks, and vegetation, and can travel at high speeds, causing considerable damage.
Slide: a slide refers to a type of mass wasting or mass movement where material moves downslope along a distinct surface. Unlike a slump, which involves rotational movement along a curved surface, a slide typically involves movement along a well-defined plane or surface.
Slump: Slump occurs when a portion of the slope moves as a single mass along a curved surface. It typically happens in cohesive materials, such as clay or silt, when the lower part of the slope becomes saturated and loses its strength. The sliding material rotates backward along the curved surface, creating a distinctive step-like feature.
Landslide: Landslides are rapid and often catastrophic mass movements involving a sudden and widespread collapse of a slope. They can be triggered by intense rainfall, earthquakes, or human activities. Landslides can vary in size, from small and localized debris flows to large and devastating avalanches of rock and soil.
Rockfall: Rockfalls occur when individual rocks or boulders detach from a steep slope and freefall or bounce down the slope. They often happen due to weathering and erosion, which weaken the rocks' connection to the slope. Rockfalls pose a significant hazard to people and infrastructure in mountainous areas.
Using the information above and your observation on the ground, you should be able to discern the type of mass wasting that has occurred here.