DRRR 2nd Semester: Geological Hazards

• Geological hazards are natural processes that threaten human life and infrastructure.
• The lesson is for the second semester of DRRR.

Geological Hazards

• These are natual events cause major problems globally.
• Aside from earthquakes and volcanic eruptions, other related hazards can cause minor to major destruction.
• Natural phenomena cause problems all over the world.

Learning Outcomes

• Discuss the different geological hazards.
• Analyze the causes of geological hazards.
• Recognize the signs of impending geological hazards.
• Interpret different geological maps.
• Apply mitigation strategies to prevent loss of lives and properties.

Earthquake

• Earthquakes are from the sudden movement of tectonic plates in the Earth's crust.
• Earthquakes can result in ground shaking, ground displacement, landslides, liquefaction, and tsunamis.
• The severity of earthquakes is measured using the Richter Scale, ranging from 1 to 10.

Landslide

• Landslides happen when soil and rock slide down a slope due to gravity.
• Triggers include heavy rain, earthquakes, volcanic eruptions, deforestation, and construction.
• Landslides can cause damage to infrastructure and loss of life.

Tsunami

• Tsunamis are large ocean waves which are triggered by seismic events, volcanic eruptions, and landslides.
• Tsunamis cause widespread destruction, loss of life, and damage to infrastructure, especilly in coastal areas.

Sinkholes

• Sinkholes are depressions or cavities in the ground occurring when soil or rock collapses.
• Sinkholes can be caused by natural processes like erosion or human activities like mining and groundwater pumping.
• Sinkholes can cause damage to infrastructure and loss of life.

Types of Sinkholes

• Dissolution Sinkholes
• Cover-subsidence Sinkholes
• Cover-collapse Sinkholes

Rockfalls

• Rockfalls occur when rocks detach from a slope and fall.
• Triggers include earthquakes, weathering, mining, and construction.
• Rockfalls cause damage to infrastructure and loss of life.

Natural Causes of Landslides

• Groundwater (pore water) pressure.
• Erosion of the toe of a slope by rivers or ocean waves.
• Loss or absence of vertical vegetative structure, soil nutrients, and soil structure (ex: wildfire).
• Weakening of a slope through saturation by snow, glaciers, melting, or heavy rains.
• Earthquakes are adding loads to barely stable slopes.
• Earthquake-caused liquefaction destabilizes slopes.
• Volcanic eruptions.

Human Activities Aggravate Landslides

• Deforestation.
• Cultivation.
• Construction can destabilize fragile slopes.
• Vibrations from machinery or traffic.
• Blasting.
• Earthwork.
• Removal of deep-rooted vegetation.
• Construction, agricultural, or forestry activities.

Landslide Characteristics

• Landslides are massive outward and downward movement of slope-forming materials.
• A landslide is caused by earthquakes or volcanic eruption as a geological hazard.
• The term "landslide" is restricted to movements of rocks and soil masses.
• Movements can range in size up to entire mountainsides.
• It is initiated when a section of hill slope or sloping section of a sea bed is rendered too weak to support its own weight.

Rainfall-Induced Landslide

• It is a massive outward and downward movement of slope forming materials.

Effects of Landslides

• Property damage.
• Injury and death.
• Adversely impact a variety of resources such as water supplies, fisheries, and roadways.
• Negative economic effects include repair costs, loss of property value, and medical costs.

Sinkholes

• Sinkholes are common where the rock below the surface is limestone, carbonate rock, salt beds, or rocks dissolvable by groundwater.
• Sinkholes can be human induced by groundwater pumping, construction and development practices.
• Sinkholes can also form when natural water-drainage patterns are changed, and new water diversion systems are developed.
• Sinkholes can form when the land surfaces is changed, such as when industrial and runoff-storage ponds are created.
• The weight of the new material can trigger an underground collapse, thus causing a sinkhole.

Dissolution Sinkholes

• Occur where water first contacts the rock surface with greatest intensity.
• Flow focused in pre-existing openings, joints, fractures, and bedding planes.
• Dissolution also occurs in the zone of water-table fluctuation where groundwater is in contact with the atmosphere.

Cover-Subsidence Sinkholes

• Develop where covering sediments are permeable and contain sand.
• If cover material is thicker or sediment has clay, cover-subsidence sinkholes are relatively uncommon, smaller, and undetected for long periods.

Cover-Collapse Sinkholes

• Develop abruptly over hours and cause catastrophic damages.
• They happen where covering sediments contain significant amounts of clay.

Signs of Impending Landslide

• An earlier landslide is an indicator.
• Tension cracks form.
• Things such as trees are moving.
• Water is behaving differently.

Landslides in Recent Past

• Cherry Hills, Antipolo Rizal, August 3, 1999.
• 2024 Catastrophic Landslide struck Barangay Masara in Maco, Davao de Oro, Philippines, following days of relentless heavy rainfall.
• 2006 The entire village of Guinsaugon in St. Bernard, Southern Leyte was buried after a portion of a nearby mountain collapsed.

Signs of 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, slopes that appear in a yard
• Dead patches of grass or plants
• Sinkholes nearby
• Wilted vegetation in a limited area
• Discolored well water
• Cracking or buckling of a home's concrete slab
• Presence of odd bugs
• Earthy odor after rain
• New or widening cracks
• Doors and windows don't open or close easy
• Separation between walls and ceiling or floors
• Cracks around door and window frames
• Cracked grout and tiles
• Stair step cracks in blocks or bricks
• Uneven floors, warping of hardwood, bulging or sagging sections
• Cracks in sheetrock near doors or windows