Hazard Maps and Landslides Overview

Hazard Maps

• Hazard maps identify areas prone to natural hazards such as earthquakes, floods, volcanic eruptions, landslides, liquefaction, and tsunamis
• Maps are crucial for community resilience, earthquake hazard prediction, zonation mapping, vulnerability assessments, and mitigation measures
• Hazard maps support land-use zoning, engineering measures for structural strengthening, and efficient resource allocation

Landslides

• Landslides are movements of rock, debris, or earth due to gravity
• Common forms include falls, topples, slides, spreads, and flows like mudflows and rockfalls.
• Rainfall, snowmelt, changes in water levels, earthquakes, volcanic eruptions, and human activities drive landslides
• Warning signs of an impending landslide:
  • Presence of water in areas not usually wet
  • New cracks or ground bulging
  • Soil movement from foundations
  • Cracking and tilting of structures
  • Broken pipes
  • Leaning posts, trees, or fences
  • Sunken roadbeds
  • Decreased water levels in nearby streams
  • Unusual rumbling sounds
• Landslide prevention strategies:
  • Hazard mapping to avoid landslide-prone areas
  • Public information and awareness campaigns
  • Engineering interventions like improved drainage and retaining walls
  • Slope protection measures using coconut bioengineering, shotcrete, or gabion walls
  • Vegetation preservation and early warning systems

Earthquake Effects

• Earthquakes generate P-waves and S-waves (body waves) and Love waves and Rayleigh waves (surface waves)
• The Richter scale measures earthquake magnitude
• Ground movement (ground shaking) intensity depends on distance from the epicenter and ground material
• Loose sediments are more susceptible to damage than solid rock during earthquakes
• Earthquakes cause ground rupture along fault lines, damaging buildings and infrastructure
• Secondary effects of earthquakes:
  • Fires caused by damaged power lines and gas pipes
  • Rapid mass movement like landslides, rockfalls, and slumps
  • Liquefaction where water-saturated sediments lose strength, causing the ground to behave like liquid
  • Aftershocks: Subsequent smaller earthquakes after the main event

Tsunami

• Tsunamis are large ocean waves caused by earthquakes, landslides, or volcanic eruptions
• Tsunamis can travel quickly, up to 725 km/h
• Tsunamis cause significant damage and flooding in coastal areas

Volcanic Eruptions

• Types of volcanic eruptions:
  • Effusive eruptions: Less viscous magma flows out as lava, with minimal explosions due to easy gas expansion
  • Explosive eruptions: High-viscosity magma causes gas bubbles to build up pressure, leading to explosions and pyroclastic material
  • Lava flows: Molten rock flowing down slopes
  • Fissure eruptions: Magma erupts along Earth's surface cracks or fissures
  • Underwater eruptions: Produce pillow lavas
• Secondary effects of volcanic eruptions:
  • Lava flows damage buildings and property
  • Volcanic ash causes respiratory problems and infrastructure damage
  • Toxic gas releases endanger life and property

Types of Volcanic Eruptions

• Lava dome: Highly viscous, low gas content lava piling up over a volcanic vent
• Explosive eruptions (e.g., Plinian):
  • Clouds of gas and tephra rise above the volcanic crater, forming a column up to 45 km high
  • Tephra is carried by wind over long distances
  • Example: The 79 CE eruption of Mt. Vesuvius killed approximately 20,000 people in Pompeii
• Phreatic eruptions:
  • Magma heats groundwater, producing steam that blasts through surrounding rock or sediment
  • Eruption column height typically around 100 meters
  • Mildly explosive, known as Strombolian eruption
• Pyroclastic flows (Nuée Ardente):
  • Lateral blasts of material along the lava dome

Hazards of Volcanic Eruptions

• Pyroclastic flows: Hot, high-speed currents of ash, gas, and rock
• Lahars: Volcanic mudflows formed when volcanic material mixes with water (rainwater, melted ice, or crater lake drainage)
• Ash falls: Volcanic ash damages property and poses respiratory hazards
• Toxic gases: Volcanic eruptions release toxic gases like water vapor, HCl, H2S, SO2, HF, CO2, Cl, S, and F, with disastrous effects on organisms
• Lava flows: Common in Hawaiian and Strombolian eruptions
• Debris avalanches and flows: Secondary effects of eruptions
• Landslides: Can be triggered by volcanic eruptions
• Flooding: Occurs upon blockage of drainage systems
• Tsunamis: Large waves generated by eruptions, like the 1883 Mt. Krakatau eruption (Indonesia), which caused 36,400 deaths in regions far from Krakatau
• Volcanic earthquakes: Occur during volcanic events

Specific Examples of Volcanic Eruptions

• 1991 Mt. Pinatubo eruption: Produced lahars and caused significant loss of life and property
• 1883 Mt. Krakatau eruption: Generated substantial tsunamis and widespread damage

Global Impact of Volcanic Eruptions

• Mt. Pinatubo eruption released large amounts of gases and aerosols, leading to a temporary drop in average global temperature of about 0.6 degrees Celsius for 15 months

Lesson 8: Geological Processes and Hazards

• The Philippines frequently experiences earthquakes, volcanic eruptions, and landslides due to its geographic location
• The Sendai Framework (2015-30) emphasizes understanding disaster risk for effective management
• Disaster risk includes vulnerability, capacity, exposure of people and assets, hazard characteristics, and the environment
• Earthquakes are caused by sudden energy release from strained rocks beneath the surface
• When rocks fracture, vibrations are created and propagate as seismic waves
• Elastic Rebound Theory: Explains strain energy buildup and sudden release in rocks around a fault
• Focus (or Hypocenter): Location of fracture during an earthquake
• Epicenter: Location on the surface directly above the focus

Lesson 10: Marine and Coastal Processes and Their Effects

• Coastal environments vary in structure, topography, climate, and living organisms they host
• Continental and oceanic processes create geologic features prone to rapid change
• Plate tectonics greatly influences coastal topography
• Coastal Hazards:
  • Powerful coastal currents, including rip currents and tidal currents
  • Coastal erosion causing property damage
  • Storm surge from tropical and extratropical cyclones
  • Tsunamis, especially threatening coasts around the Pacific Ocean

Waves and Coastlines

• Waves are generated by offshore winds, transferring energy to the water
• Wave size and shape depend on wind speed, duration, and fetch (distance wind blows across the water)
• Interactions between multiple wave sets produce regular patterns
• Open Sea: Storm-generated waves are swells, becoming dangerous in shallow water
• Shallow Water: Swells lose stability and break on the shore
• Headlands: Waves bend (refract) and become parallel to the shoreline, reducing erosion on rocky peninsulas
• Breaking Waves: Plungers (erosive), surgers, or spills (depositing sand), depending on beach slope and topography

Beaches and Coastal Processes

• Beaches are accumulations of sand, gravel, and other material from continuous wave action
• The swash zone is the area where waves uprush and backwash
• Beach location varies with storms and tides
• Aquatic Zones:
  • Surf Zone: Highly energetic waves after breaking waves
  • Breaker Zone: Unstable waves that peak and break, with a longshore bar forming beneath the breakers
• Sand Movement: Waves continuously transport sand within the surf and swash zones
• Storms erode sand from beaches, redepositing it offshore; it often returns after weather conditions improve

Other Coastal Processes

• Littoral Transport: Sediment movement within the littoral zone (beach area)
• Global Impact of Waves: Waves influence water volume and coastal regions

Coastal Processes and Hazards

• Littoral Transport includes beach drift (zigzag movement of sediment) and longshore drift (sediment movement parallel to the shoreline)
• Sea level changes, influenced by local, regional, and global factors, affect the relative sea level
• Global Sea Level Change: Eustatic sea level, determined by ocean water volume and ocean basin characteristics, can lead to submerged coastal areas
• Coastal erosion damages beaches, cliffs, dunes, and human-made structures
• Coastal Hazards: Strong currents, storm surges, and tsunamis are intensified by coastal erosion
• Erosion Mitigation: Engineering solutions like seawalls, groins, breakwaters, and jetties. Beach nourishment adds sand to eroded beaches
• Freshwater-Saltwater Interface: The boundary between fresh groundwater and saltwater is a mix zone
• Saltwater Intrusion: Excessive groundwater pumping can cause saltwater to intrude into freshwater aquifers, contaminating water sources

This quiz covers the essential concepts of hazard maps, highlighting their role in identifying areas vulnerable to natural hazards like landslides and earthquakes. It delves into the mechanisms behind landslides, including driving factors and key warning signs. Understanding these concepts is crucial for risk assessment and community preparedness.