DRRR - Geological Hazards

Geological Hazard

natural phenomena and an adverse geologic condition capable of causing widespread damage or loss of property and life. These hazards are geological and environmental conditions and may result in short-term or long-term geological processes.

Types of GeoHazard

Landslides, and Sinkholes

Landslide

the movement of rock, soil, or debris down a slope due to gravity. It can be triggered by natural causes like heavy rain, earthquakes, volcanic activity, or human activities such as deforestation and construction. They can cause significant damage to buildings, roads, and the environment.

Types of Landslides

Soil Creep, Slumping, Debris Flow, Rock Fall

Soil Creep

• This is the slowest type of landslide.

• It involves the gradual, downhill movement of soil and regolith.

• It's often difficult to notice directly, but its effects can be seen over time (e.g., tilted fences, and curved tree trunks).

• Causes include gravity, freeze-thaw cycles, and wetting-drying cycles.

Slumping

• This type of landslide involves the movement of a mass of soil or rock along a curved, concave surface.

• The slumped material often remains relatively intact as it moves.

• It creates a characteristic "spoon-shaped" depression.

• Often triggered by heavy rainfall or slope undercutting.

Debris Flow

• This is a rapid flow of water, rock, soil, and debris.

• It's often triggered by intense rainfall or rapid snowmelt.

• Debris flows can travel at high speeds and carry large boulders and other debris.

• They commonly happen in channels and can travel significant distances.

• They are very dangerous.

Rock Fall

• This involves the freefall of rocks from a cliff or steep slope.

• It's a very rapid and dangerous type of landslide.

• Often triggered by weathering, erosion, or earthquakes.

Guinsaugon Landslide

Occurred at the Municipality of St. Bernard, Southern Leyte Province, Philip­pines, at about 10:30 local time on February 17, 2006. According to the Philippines Office of Civil Defense, up to 2,000 people may have been buried, including 250 children in the local school.

Sinkhole

Depression in the ground that form when uderlying rocks dissolve or collapse. They are caused by groundwater erosion or the collapse of underground cavities. It damages infrastructures, homes, and even cause injuries or fatalities.

Types of Sinkholes

Cover Collapse, Cover Subsidence, Dissolution , Artificial

Cover Collapse

• Form suddenly and dramatically when the soil layer above an underground cavity collapses.

• Occur in areas with thick clay or cohesive soils that can temporarily support a growing underground void.

• Water seeps through cracks, enlarging an underground cavity until the weight of the overlying material is too great.

Cover Subsidence

• Develop gradually rather than collapsing suddenly.

• Soil slowly seeps downward into cracks and voids in the rock below, creating a gradual depression at the surface.

• Typically shallow and bowl-shaped rather than deep and abrupt.

• More common in areas with thin soil cover and frequent water infiltration.

Dissolution Sinkhole

• Caused by the direct chemical dissolution of soluble bedrock, such as limestone, gypsum, or salt.

• Common in areas with thin or absent soil cover, where bedrock is exposed or near the surface.

• Can expand over time as more rock dissolves, increasing their depth and width.

Artificial Sinkhole

• Caused by human activities that disturb the underground structure or water table.

• These sinkholes can be prevented with proper land-use planning and engineering solutions.

Itogon, Benguet Sinkhole

It occurred on October 22, 2015, several days after a Typhoon. It was 20 meters deep and along Batuang Road. A mining hole 90 Meters under the sinkhole was discovered, which experts say may have contributed even more to its occurrence.

Causes of Landslides and Sinkhole

Natural Causes, Humanitarian Causes

Natural Geological Causes of Landslides and Sinkholes

• Weak or sensitive materials

• Weathered materials

• Sheared, jointed, or fissured materials

• Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, contact, etc.)

• Contrast in permeability and/or stiffness of materials

Natural Morphological Causes of Landslides and Sinkholes

• Tectonic or volcanic uplift

• Glacial rebound

• Fluvial, wave, or glacial erosion of slope toe or lateral margins

• Subterranean erosion (solution, piping)

• Deposition loading slope or its crest

• Vegetation removal (by fire, drought)

• Thawing

• Freeze-and-thaw weathering

• Shrink-and-swell weathering

Humanitarian Causes of Landslides and Sinkholes

• Excavation of slope or its toe

• Loading of slope or its crest

• Drawdown (of reservoirs)

• Deforestation

• Irrigation

• Mining

• Artificial vibration

• Water leakage from utilities

Warning Signs of an Impeding Landslide

• Earlier landslide as indicator

• Things Moving

• Water Doing Something Different

Earlier landslide as indicator

• Frequent landslides in an area suggest weak and unstable soil, making it more susceptible to landslides.

• Causes include lack of vegetation, weathering, erosion, etc.

• Multiple landslides in the same place can be retrogressive, piecemeal, or reactivated.

• A reactivated landslide occurs when an old, semi-stable landslide changes, causing a new collapse.

• Inspecting old landslide areas for scarps and deposits indicates potential reactivation, showing the region's geology is fragile and vulnerable.

Things Moving

• Non-living objects moving without human intervention can indicate a landslide.

• Trees forming a J-curve signify the ground slipping beneath them.

• Patches of angled forest on a slope can indicate unstable ground.

• Doors no longer closing properly and broken utilities.

• Movement of floor tiles, deformation of door frames, and broken electric posts, gas, water, and sewage pipes.

• Creaking and cracking sounds can be warning signs of a landslide.

Water Doing Something Different

• Springs, seeps, or wet ground appearing in previously dry terrain can indicate water presence or withdrawal.

• Water alters pressure within slopes, contributing to instability.

• Debris flow is a wet, mobile landslide carrying water, trees, mud, rocks, and other debris.

• Low water levels precede debris flow surges, indicating potential danger

Warning Signs of an Impending Sinkhole

• Trees or fence posts that tilt or fall

• Foundations that slant

• New small ponds that appear after rain

• Cracks in the ground

• Sudden drainage of a pond

• Rapid appearance of a hole in the ground

• Dips, depressions, and slopes that appear in a yard

Warning Signs of an Impending Sinkhole

• Dead patches of grass or plants

• Sinkholes in the neighbourhood

• Wilted vegetation in a limited area

• Well water that is discolored or contaminated with debris

• Cracking or buckling of the home’s concrete slab

• Presence of odd bugs like slugs, and centipedes in homes

• Earthly odor in home after rain

• New or widening cracks

Warning Signs of an Impeding Geological Hazard

• Separation between walls and ceiling or floors

• Cracks around door and window frames

• Cracked grout between tiles

• Cracked tiles

• Stair step cracks in blocks or bricks

• Uneven floors, warping of hardwood, bulging or sagging sections

• Doors or windows that don’t open or close easily

• Cracks in sheetrock near doors or windows

Hazard Map Legend

• Red

• Orange

• Green

• Yellow

• Purple

Hazard Map Legend - Red

Very high Susceptibility to Landslide

Hazard Map Legend - Orange

High Susceptibility to Landslide

Hazard Map Legend - Green

Moderate Susceptibility to Landslide

Hazard Map Legend - Yellow

Low Susceptibility to Landslide

Hazard Map Legend - Purple

Debris Flow/Possible Accumulation Zone

Mitigation

involves acting to reduce the risk of life or
property damage from a potentially dangerous incident.
There is no way to avoid natural disasters, but people
and organizations may take steps to minimize the harm
and losses that they cause.

Programs to intensify Mitigation

• Protection of schools and hospitals

• Adoption of nonstructural measures

• Incorporation of mitigation into new development

• Protection of cultural properties

• Protection of natural resources

• Government leadership of mitigation
  implementation

• Mitigation training

• Hazard-specific research

Mitigation and Preventive Measures Before Landslides

• Be familiar with your surroundings

• Avoid open storm-water drainage and runoff

• Be updated on news regarding the condition of your area

• Be aware of the disaster plans of your local government

• Learn and participate in emergency response and
  evacuation plans for your community.

Mitigation and Preventive Measures During Landslides

• Be attentive to unusual such as cracking objects, moving
  debris, and rolling boulders.

• Stay away from the path of debris

• Stay alert and awake

• Stay on an elevated and sturdy area

• If escape is not possible, curl into a tight ball and protect
  your head

Mitigation and Preventive Measures After Landslides

• Stay away from a slide area as there is still danger of more
  landslides

• Listen for the latest emergency information

• Follow warnings and instruction from the local government

• If the landslide is caused by rainfall, watch out for flooding
  as it will follow the same path taken by the debris flow

• Check for injured or trapped people near the slide, and
  flooding as it will follow other potential hazards. Report
  these immediately to the rescuers or authorities

Mitigation and Preventive Measures for Sinkholes

• Find refuge in a stable ground or open area.

• Wait until the structures on and around it stops
  moving. Do not attempt to go back and retrieve your belongings.

• Wait for the local government’s announcement when it is safe
  to go back.

Mitigation and Preventive Measures for Sinkholes

• Stay away

• Monitor the damage to objects

• Do not throw anything inside

• Secure whatever is left of your properties and relocate to
  safe grounds, preferably far from this location because the
  same bedrock or soil profile may characterize the vicinities
  of the sinkhole