Disaster Readiness and Risk Reduction Notes

Disaster Readiness and Risk Reduction: Other Related Geologic Hazards

Unit Overview

  • This unit discusses different geological hazards, their causes, signs, and mitigation strategies for preventing loss of lives and properties.

Learning Targets

  • Discuss the different geological hazards.

  • Analyze the causes of geological hazards.

  • Recognize signs of impending geological hazards.

  • Interpret geologic maps.

  • Apply mitigation strategies to prevent loss of lives and properties.

Lesson 1: Ground Subsidence

Causes and Effects

  • The Philippines is highly vulnerable to natural disasters like floods, typhoons, landslides, earthquakes, volcanoes, and droughts due to:

    • Location at the intersection of two main tectonic plates.

    • Position within a typhoon belt.

  • The Philippines is among the top three nations for population exposure and hazard vulnerability.

  • The government has developed coping methods due to its history of dealing with disasters.

  • There are gaps in disaster management capabilities across different regions.

  • Local disaster preparedness and resilience information is extremely limited.

Central Question

  • What is the difference between the preparation for hydrometeorological and geological hazards?

Ground Subsidence: A Silent Hazard

  • Ground subsidence is a phenomenon where the land gradually or suddenly sinks.

  • It is caused by excessive water extraction below the ground, which the environment cannot replenish quickly enough.

  • From 1979 to 2009, some areas in Metro Manila sank 0.68 meters to 1.34 meters.

  • CAMANAVA (Caloocan City, Malabon City, Navotas City, and Valenzuela City) is affected by groundwater subsidence due to excessive groundwater pumping by fishpond operators.

  • Continued sinking may cause dikes protecting CAMANAVA from seawater incursion to be overtopped, leading to unexpected floods.

What Is Ground Subsidence?

  • Ground subsidence, including sinkholes, can result from excessive groundwater extraction in urban areas.

  • Sinkholes form in karst terrain, characterized by bedrock made of limestones, dolomite, or gypsum.

Types of Sinkholes

  • Dissolution Sinkholes: Occur where bedrock is exposed or very shallow, resulting from rainfall and surface water.

  • Cover-Subsidence Sinkholes: Develop gradually where covering sediments are permeable and contain sand.

  • Cover-Collapse Sinkholes: Occur in soil or loose material overlying soluble bedrock.

  • Human-Induced Sinkholes: Result from land use practices, especially construction and water pumping.

Causes of Ground Subsidence

  • Natural processes or human activities can cause ground subsidence.

  • Dissolution and diversion of natural water drainage patterns or dewatering.

  • Compaction of soil.

  • Subterranean mining.

  • Thawing permafrost.

Effects of Ground Subsidence

  • Impacts agricultural lands, industrial processes, and infrastructure.

  • Farmlands, irrigation systems, and groundwater wells can be destroyed.

  • Infrastructures on subsiding ground can be damaged or destroyed.

  • Mining areas, tunnels, and surrounding areas can collapse.

  • Can cause injuries and fatalities.

Tips to Mitigate Ground Subsidence

  • Find alternative sources of groundwater.

  • Avoid building infrastructure near land fissures.

  • Route drainage away from cracks.

  • Prohibit residential zones in or near fissure areas or ground with high subsidence susceptibility.

Lesson 2: Rainfall-Induced Landslide

What is Rainfall-Induced Landslide?

  • Rainfall-induced landslide involves downslope movement of soil, rock, and organic materials due to gravity.

  • It also refers to the resulting landform from such movement.

Factors That Influence Landslide Development

  • Morphological factors

  • Geological factors

  • Human factors

  • Water (rainfall)

  • Seismic activity

  • Volcanic activity

Major Types of Landslides

  • Fall: Material on cliffs or steep slopes loses support or becomes fractured.

  • Topple: A block of material detaches from a steep slope and rotates forward and downward.

  • Slide: A detached mass of rocks, soil, and organic matter moves along a downward-sloping surface.

  • Flow: Materials from gentle slopes detach and flow like a viscous liquid.

    • Includes debris flow

    • Debris avalanche

    • Earth flow

  • Spreads: Mass of soil or rocks extends or spreads laterally.

Types of Landslides (Detailed)

  • Rotational Landslide: Ground rotates and slides along a curved failure plane.

  • Translational Landslide: Ground slides with little rotation along a flat plane parallel to the surface.

  • Block Slide: A type of translational landslide made of mostly one block of surface material that moves downslope.

  • Rockfall: Pieces of a cliff or rock face fall forward as large blocks due to gravity.

  • Earthflow: Forms on moderate slopes when fine-grained material liquefies and runs out in an hourglass shape.

  • Lateral Spread: Surface material extends or spreads on gentle slopes, often associated with earthquake shaking.

  • Debris Flow: Rapidly moving mix of water, mud, trees, and other materials that flows downvalley.

  • Debris Avalanche: An extremely large and fast-moving debris flow.

  • Creep: Soil and surface material that slowly moves down a slope.

Best Practices for Landslide Mitigation

  • Hazard mapping

  • Public information

  • Engineering intervention measures of slope protection measures

  • Early warning system (EWS)

Lesson 3: Coastal Erosion

What Is Coastal Erosion?

  • Coastal Erosion involves breaking and removing materials from the coastline due to wave action, tidal currents, and human activities.

Types of Coastal Erosion

  • Mechanical erosion of waves

  • Bioerosion

  • Weathering

  • Mass Movements

Factors That Influence Coastal Erosion

  • Lithology of rocks

  • Climate

  • Global sea level rise

  • Man-made interventions

Lesson 4: Bolide Impact

What Is Bolide Impact?

  • A bolide is a generic term for celestial bodies entering the Earth's surface and creating a fireball.

  • A superbolide is a relatively larger bolide that can cause cratering impacts.

  • Superbolides can increase the incidence of climate change and sea-level change.

Near-Earth Objects (NEOs)

  • Near-Earth Objects (NEOs) define the rocky or metallic asteroids and icy comets between Jupiter and Mars.

Hazards of Bolide Impact

  • Increased incidence of climate change and sea-level change.

  • Intense tectonic activities, earthquakes, and increased volcanism.

  • Trigger global mass extinction and global environmental dangers.

Deflection Techniques

  • Use a laser beam to move the NEO.

  • Use large lenses or mirrors to refocus the sun’s energy on a NEO.

  • Use another object to collide with a NEO to deflect or change its velocity.

Integration Steps for Bolide Impact Analysis

  • Step 1: Search for pictures of celestial bodies entering the Earth’s surface.

  • Step 2: Enumerate the possible hazards they may cause.

  • Step 3: Compare the hazards based on the rock’s sizes and shapes if they enter the Earth’s surface.

Project NOAH Integration: Fireball vs. Bolide

  • A fireball is a very bright meteor, generally brighter than magnitude -4 (same magnitude as Venus).

  • A bolide is a special fireball that explodes in the atmosphere with a bright flash before impacting the Earth and is often observed with visible fragmentation.

Perspectives in DRRR (Disaster Risk Reduction and Management) in the Philippines

  • The Philippines is located in the Pacific Ring of Fire and the typhoon belt, making it one of the most hazard-prone countries.

  • The country experiences natural hazards like earthquakes, volcanic eruptions, typhoons, floods, and droughts.

  • These hazards can be classified as geophysical disturbances, meteorological and hydrological events, and slow-onset disasters.

  • Due to increasing population and urbanization, natural disasters have resulted in unprecedented devastation.

  • From 2001 to the present, the country experienced some of the most destructive disasters, including Typhoon Yolanda and the Bohol Earthquake in 2013.