Volcanic Hazards and Flows

• Notes on Disaster Readiness and Risk Reduction

Earthquake

• Sudden ground movement releasing elastic energy stored in rocks.
• Generates seismic waves.

Ground Shaking

• Ground vibration felt when stress applied to the lithosphere is released during an earthquake.

Seismic Waves

• Elastic energies that travel through Earth's layers.
• Seismic waves are energy waves caused by sudden rock breakage or explosions within the earth.
• Travel through the earth and are recorded on seismographs.

Types of Seismic Waves

• Body Waves: Travel through Earth's interior, from the focus to distant surface points.
• P Waves: Fastest seismic wave, first to arrive at a seismic station.
  • Moves through solid rock and fluids.
  • Moves by pushing and pulling rock.
• S Waves: Second wave felt in an earthquake, slower than P waves.
  • Moves only through solid rock.
  • S waves move rock particles up and down or side-to-side, perpendicular to the wave's direction.
• Surface Waves: Travel only along the Earth's surface.
  • Love Wave: Moves rocks horizontally, side to side. Transverse, without vertical motion.
  • Rayleigh Wave: Causes rocks to move up, backward, down and ground roll. Transverse.

Measuring Ground Shaking

• Strength is measured by frequency content of shaking, velocity, acceleration, and duration.
• Intensity depends on earthquake magnitude, depth of focus, epicenter distance, and shaking duration.

Ground Rupture

• Earthquake faults that reach the surface.

Faulting

• Displacement of rocks along a fracture surface.
• Normal Fault: Hanging walls move down relative to the footwall due to extension.
• Reverse Fault (Thrust): Hanging walls move up relative to the footwall due to compression and are the most dangerous.
• Strike-Slip Fault: Blocks of crust slide past each other on the same plane.
  • Motion is right or left lateral.

Minimizing Ground Rupture Effects

• Use sound engineering and construction practices.
• Avoidance of active fault traces and high-risk danger zones.
• Look for local Active Faults. Safe distance of 5 meters from the fault is recommended.

Liquefaction

• Water-saturated sediment loses strength and acts as a fluid.
• Flow Failure: Occurs on liquefiable slope material with steepness. Most dangerous type
• Lateral Spread: Blocks or broken pieces of flat ground spreading.
• Ground Oscillation: Ground oscillates like a wave, surface layer is thrown back and forth.
• Loss of Bearing Strength: Loss of sediment strength, leading to tilting of buildings.

Settlement

• Ground failure causes buildings to shift, tilt, stretch, twist, buckle, or a combination of these.

Effects of Liquefaction

• Sinking of buildings and vehicles.
• Ground sinking, spreading, and cracking.
• Water seepage leading to flooding.

Mitigating Liquefaction

• Use hazard zone maps.
• Build liquefaction-resistant structures.
• Improve existing soil.

Landslide

• Movement of rock or debris down a slope.

Landslide Causes

• Factors include removal of support at the base of a slope.
• Changes in groundwater pressure.
• Volcanic eruption. Force of material ejection or emission and bulging of slopes.
• Intense Rainfall: Weakening of slope by water saturation.
• Snowmelt: Same effect as rain.
• Earthquake shaking.
• Human intervention.

Types of Landslides

• Topples: Part of steep slope breaks loose and rotates forward.
• Rock Falls: Detached rocks fall or bounce down a slope.
• Slides: Large bedrock blocks slide down a surface.
• Lateral Spreads: Triggered by earthquakes slope material loses cohesion from liquefaction.
• Flows: Soil motion caused by water saturation.
  • Includes mudflows and earthflows.
• Complex Slides: Combination of two or more movement types.

Controlling Factors in Mass Wasting

• Slope Angle: Increased angle increases the sliding tendency. Shear stress exceeding shear strength causes movement.
• Role of Water: Water adds weight to the slope and makes it less stable.
• Role of Earth Materials: Weak rocks weather more quickly than hard rocks.
• Role of Time: Weathering weakens slope materials and decreases resisting force.

Effects of Landslides

• Loss of lives.
• Injuries.
• Damage to structures.
• Alteration of agriculture and natural ecosystems.
• Relocation of populations and infrastructure.

Mitigating Effects of Landslides

• Report signs of slope instability and prevent construction on unstable slopes.
• Planting deeply-rooting trees to hold soil.
• Landslide barriers and drainage structures.

Tsunami

• A series of waves caused by displacement of a large water volume.

Causes of Tsunami

• Vertical fault movement that disturbs surrounding water.
• Landslides displacing ocean water.
• Volcanic eruptions or coastal explosions displacing ocean water.
• Meteorites impacting the ocean.

How to Escape a Tsunami

• Evacuate quickly.
• Know the evacuation center.
• Use safe escape routes.
• Cling to floating objects, stay alert.

How to Prepare for a Tsunami

• Treat earthquakes as natural warnings.
• Keep a radio and survival kit.

Notable Tsunamis

• 9.1 magnitude Sumatra, Indonesia, December 26, 2004
• 9.0 magnitude North Pacific Coast, Japan, March 11, 2011
• 7.9 magnitude Moro Gulf Tsunami, Western Mindanao, August 17, 1976

Effects of Tsunami

• Loss of life, property, and environmental damage. Drowning, building collapse and electrocution.

Mitigating the Effects of Tsunami

• Public information campaigns.
• Protecting properties by banning construction, building seawalls.
• Designing tsunami-resistant buildings.

Volcanic Hazards

• Probability of a volcanic eruption in a specific area within a timeframe.

Lava Flow

• Molten rock or magma flowing from a volcano, which can be from 700 to 1,200 degrees Celsius. Has extremely low speed
• As magma rises, gas expands, leading to magma's explosive character.
• The amount of gas determines the eruption type and landform, influenced by viscosity.

Composition and Temperature of Volcanoes

• High silica content leads to higher viscosity.
• Decreasing magma temperature increases viscosity.
• Low viscosity results in least explosivity.

Types of Lava Flow

• Basaltic Lava: Fastest, associated with shield volcanoes.
  • Lava Flow Styles:
    • Pahoehoe: Smooth surface.
    • A'a: Sharp, spiny surface.
• Andesitic Lava: Associated with stratovolcanoes, forms lava domes
• Rhyolitic Lava: Slower, associated with violent eruptions.
• Sheet Lava: Thicker than Pahoehoe, violent eruptions.
• Pillow Lava: Pillow-shaped rocks formed by sudden cooling.

Effects of Lava Flow

• Destroys land and property by burying, crushing, or burning and deaths from molten spatter.

Mitigating Lava Flow

• Stay away from danger zones.
• Divert lava flow using explosives and barriers.

Volcanic Gases

• Emitted by active volcanoes. Principal Components:

• Water Vapor.

• Carbon Dioxide: Abundant.

  • 2-3% causes Shortness of breath.

• 7% causes Headache, shortness of breath and ringing in ears.

• 10% Loss of conscienceless

• >15% Lethal

• Sulphur Dixoide: Colurless gas with a strong odour

  • 6-12 ppm:Irratation of nose and throat. In extreme conditions Hydrocloric Acid.

• Hydrogen Sulfide: a colurless,flammdble gas with a strang addur

• Fluorine Hydrogen Halides

• Effects of Volcanic Gasses (1991 Mt, Pinatubo Ertuption) Duing very large Eruptions, SO2 Can be injecyed ti altiudes of geater thean 10km.

  • 20 min metric tons if Sulfur Dixoide Mitigating Messures for Volcanic Gasses:

• Evacution and ressitelment if affected pupilation.

• LSe if Gas MAsk

• STY in Doors, CLise with dous.

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• Hat mixture of fresh lava,gas,rash and rock
• Mobility and Speed
• Heat if its Components
• Types of pyroclastic flows

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