Why Does DMER Happen?

DMER, or Delayed Manifestation Earthslide Reactivation, is a phenomenon where a landslide occurs long after the triggering event, such as heavy rainfall or an earthquake. This can be a significant hazard, as it can cause damage to infrastructure and even loss of life. Understanding why DMER happens is crucial for developing strategies to mitigate its risks.

1. Weakened Soil Structure:

• Hydrologic Factors:
  • Prolonged rainfall saturates the soil, reducing its shear strength and making it more susceptible to failure.
  • Rapid snowmelt can also contribute to soil saturation and trigger DMER.
• Geologic Factors:
  • Soil composition, grain size, and mineralogy influence its stability. Certain soil types, such as clay-rich soils, are more prone to DMER.
  • Fractures and joints in the bedrock can provide pathways for water to infiltrate and weaken the soil structure.

2. Loss of Vegetation:

• Vegetation plays a vital role in stabilizing slopes and preventing erosion.
• Deforestation, wildfires, and other human activities can remove vegetation, making slopes more vulnerable to landslides.
• Loss of root systems reduces soil cohesion and increases the likelihood of DMER.

3. Anthropogenic Factors:

• Improper Land Use:
  • Constructing buildings or infrastructure on steep slopes without proper engineering measures can increase the risk of DMER.
  • Modifying natural drainage patterns can also contribute to slope instability.
• Excavation and Mining:
  • Removing soil and rocks for construction or mining purposes can create unstable slopes.
  • Improper disposal of spoils and waste can further exacerbate the problem.

4. Climate Change:

• Increased Precipitation:
  • Climate change is leading to more frequent and intense rainfall events, which can trigger DMER.
  • Heavier rainfall can saturate the soil more quickly, reducing its stability.
• Warmer Temperatures:
  • Rising temperatures can thaw permafrost, which can destabilize slopes and increase the risk of landslides.
  • Warmer temperatures can also lead to changes in vegetation patterns, making slopes more vulnerable to erosion.

5. Delayed Triggering Mechanisms:

• Pore Water Pressure Buildup:
  • Infiltrating water can increase pore water pressure within the soil, reducing its shear strength and triggering landslides.
  • This process can take time, leading to the delayed manifestation of DMER.
• Creep and Stress Redistribution:
  • Soil and rock can slowly deform under the weight of overlying material, a process known as creep.
  • This creep can redistribute stresses within the slope, eventually leading to failure.

Conclusion:
Understanding the causes of DMER is essential for developing effective mitigation strategies. By addressing factors such as soil stability, vegetation cover, land use planning, and climate change, we can reduce the risk of these devastating events and protect communities from their impacts.

Frequently Asked Questions:

1. What is the difference between DMER and a regular landslide?

   • DMER occurs long after the triggering event, while regular landslides typically occur during or shortly after the triggering event.

2. What are some common signs that a slope is at risk of DMER?

   • Signs include visible cracks in the ground, bulging slopes, and changes in water flow patterns.

3. Can DMER be predicted?

   • Predicting DMER is challenging, but ongoing research is improving our ability to identify areas at risk.

4. How can we mitigate the risk of DMER?

   • Mitigation measures include slope stabilization, proper land use planning, and reducing deforestation.

5. What are some examples of DMER events?

   • The Oso mudslide in Washington State in 2014 and the Slumgullion landslide in Colorado in 2018 are examples of DMER events.