Grade 12 STEM: Other Geological Hazards

Other Related Geological Hazards

• Chapter covers other geological hazards, specifically for Grade 12 students in the Science, Technology, Engineering, and Mathematics (STEM) academic track, S.Y. 2024–2025.

Other Geological Hazards and their Causes

• Geological hazards beyond earthquakes and volcanic eruptions along with their causes will be examinied.

Rainfall Induced Landslide

• Massive outward and downward movement of slope-forming materials define a landslide.
• The term "landslide" is exclusive to movements of rocks and soil masses, ranging from small size to entire mountainsides.
• Landslides are often triggered by natural hazards such as prolonged heavy rainfall, increasing water content in slope materials.

Causes of Landslides - Natural

• Groundwater pressure destabilizes slopes.
• The Loss of vertical vegetative structure, soil nutrients, after wildfires contribute to landslides.
• The erosion of a slope's toe by rivers or ocean waves can destabilize it.
• Saturation from snow melt, glacier melting, or heavy rains leading to slope weakening.
• Earthquakes add loads to barely stable slopes, causing liquefaction and destabilizing slopes.
• Volcanic eruptions contribute to landslides.

Causes of Landslides - Human Activity

• Deforestation, cultivation, and construction destabilize fragile slopes.
• Vibrations from machinery or traffic.
• Blasting (e.g., in mining).
• Earthworks alter slope shapes and impose new loads.
• Removal of deep-rooted vegetation in shallow soils.
• Changes in water infiltration from construction, agriculture, or forestry activities.

Effects of Landslides

• Landslides cause property damage, injury, and death.
• Landslides negatively impact water supplies, fisheries, waste disposal, forests, dams, and roadways.
• Landslides cause negative economic effects, including repair costs, property loss, and medical expenses.
• Landslides affect the availability, quantity, and quality of water.
• Assessing and stabilizing potentially dangerous sites with geotechnical and engineering projects is costly.

Sinkholes

• Sinkholes are common in areas where the bedrock can be dissolved by groundwater, like limestone, carbonate rock, and salt beds.
• Sinkholes occur with the underground rock dissolves which leads to underground spaces and caverns that can cause a sudden collapse of land surface.
• Sinkholes can vary in size and can affect areas where infrastructure like houses or roads are located.

Types of Sinkholes - Dissolution Sinkholes

• Dissolution sinkholes occur where water first contacts the rock surface, especially limestone or dolomite.
• Dissolution is aggressive in preexisting openings like joints, fractures, and bedding planes.
• Dissolution also occurs in the water-table fluctuation zone where groundwater meets the atmosphere.

Types of Sinkholes - Cover-Subsidence Sinkholes

• Covering sediments are permeable and sandy resulting in Cover-Subsidence sinkholes which develop gradually.
• They are relatively uncommon in areas with thicker cover or clay sediments.
• Cover-subsidence sinkholes are smaller and may go undetected for extended periods.

Types of Sinkholes - Cover-Collapse Sinkholes

• Cover-collapse sinkholes develop abruptly, often in hours, causing significant damage.
• They occur where covering sediments contain significant clay.
• Over time, these sinkholes evolve into shallower, bowl-shaped depressions due to surface drainage, erosion, and deposition.

Human-Induced Sinkholes

• New sinkholes are linked to land-use practices, specifically, new sinkholes have been correlated to groundwater pumping and construction.
• Sinkholes form when natural drainage is altered or new water-diversion systems are made.
• Industrial and runoff-storage ponds can trigger underground collapses, leading to sinkholes due to the material's weight.

Signs of Impending Geological Hazards

• Geological Hazards may be coming if you witness the following

Signs of an Impending Landslide - Earlier Landslide as an Indicator

• Old landslides indicate unstable geology and future landslide risk.
• Multiple events can be retrogressive, piecemeal, or reactivated, with reactivation occurring when changes trigger new failures in a semi-stable location.
• The presence of many old landslide scarps and deposits suggests instability in the entire region.

Signs of an Impending Landslide - Tension Cracks

• Tension cracks result from geological stress pulling material apart.
• These cracks can mark the top edge of a potential failure zone.
• Tension cracks can be identified as road segments needing frequent repairs.
• Tension cracks above an landslide suggest potential reactivation.
• On flat ground, tension cracks are more likely related to a fault.

Signs of an Impending Landslide - Things Moving

• Observable movement and deformation show of an impending landslide.
• Trees bending in J-curves show the ground is slipping.
• Angled forests or trees with J-curves suggest unstable ground.
• Catastrophic collapse may follow tension cracks farther uphill.

Signs of an Impending Landslide - Water Doing Something Different

• Changes in water as a warning sign for a landslide.
• Sudden appearance or disappearance of water in springs, seeps, or creeks points to underground changes.
• A sudden drop in creek water level shows an upstream obstruction.
• Obstructions like landslide dams could cause debris flow.
• Debris Flow is when the water is loaded with trees, mud and rocks.
• Low water warns of a coming debris flow surge.

Signs of an Impending Sinkholes

• Watch for environment signs or nearby home that indicates a problem imminent danger of sinkhole.
• Trees or fence posts tilting or falling.
• Slanting foundations.
• New small ponds appearing after rain.
• Cracks in the ground.
• Ponds suddenly draining.
• Rapidly appearing holes in the ground.
• Dips, depressions, and slopes in the yard.
• Dead grass or plant patches.
• Existing sinkholes nearby.

Warning signs of sinkholes

• Wilting vegetation in the area.
• Well water turns discolored or contaminated.
• Cracking or buckling of concrete slabs.
• Presence of slugs and centipedes, and earthy odors in the home following rain.
• New or widening cracks appear.
• Separation of walls from ceilings or floors.
• Cracks appear in interior walls, around door and window frames and in cracked grout or tiles.
• Stair step cracks in blocks or bricks.
• Warped floors of hardwood, bulging or sagging sections and doors or windows that are hard to open or close.
• Cracks in sheetrock near doors or windows.

Precautionary Measures for Sinkholes

• Signs of water disappearing from the surface need monitoring.
• It is important to Barricade areas of traffic where sinkholes occur.
• Check fields before using machinery, keep machinery far from sinkholes, machinery should be as far as the sink as the hole is deep.
• Look at times of rapid rainfall for sinkholes.
• Call emergency hotlines about sinkholes, especially if near utility lines or roadways.
• Restrict access to the sinkhole, avoid getting too close or going inside and prevent unauthorized investigations.

Before a Landslide:

• Secure information a clearance from the Mines and Geosciences Bureau (MGB) for possible landslides.
• Prepare all family members for evacuation.
• Keep a list of contact information in case of emergencies, participate in planting grasses for soil erosion prevention.
• Participate in evacuation procedures, promote awareness for landslide mitigation and encourage family preparedness and evacuation procedures.

During a Landslide:

• Immediate evacuation is critical.
• Stay away from the path of landslide debris, seek refuge behind a tree.
• When inside a house you must get out when you heart rumbling.
• Run the the the slope and not down it.

After a Landslide:

• Look for damaged parts and examine utilities and proceed cautiously.
• Stay away from any area that has additional landslides.
• Help with caution, and seek advice from a geotechnical expert to reduce risk.

Explore geological hazards beyond earthquakes and volcanic eruptions, focusing on landslides and their causes. Learn about the impact of rainfall, groundwater pressure, and erosion on slope stability. Designed for Grade 12 STEM students, S.Y. 2024-2025.