Dangerous Earth Cram

What is the Risk Equation?

Risk = Hazard × Exposure × Vulnerability

Define Hazard (risk equation)

The natural event or dangerous physical phenomenon itself, including its probability, magnitude, spatial extent, and recurrence

Define Exposure (risk equation)

The quantity of people, buildings, infrastructure, agriculture, and economic assets located directly within the hazard's footprint

Define Vulnerability (risk equation)

The physical, social, economic, or structural conditions that make exposed people or assets susceptible to harm or damage

Earthquake Hazard

Ground motion and shaking intensity caused by fault rupture (e.g., probability of a Mw7.5 earthquake in an urban area)

Earthquake Exposure

Buildings, transport networks, and urban population density situated near fault lines or soft soils

Earthquake Vulnerability

Unreinforced masonry buildings, poor structural design, or lack of earthquake drills

Earthquake Control/Reduction

Structural retrofitting,

base isolators/flexible dampers,

enforcing modern seismic building codes reduce vulnerability

Tsunami/Coastal Hazard

Tsunami wave height, ocean drawdown, storm surge, or sea-level rise

Tsunami/Coastal Exposure

Homes, businesses, and critical infrastructure built on flat, low-lying coastal plains (Hilo, Hawaii, Torres Strait Islands)

Tsunami/Coastal Vulnerability

Lack of immediate high ground, overreliance on sea walls alone, or delayed evacuations

Tsunami/Coastal Control/Reduction

Land-use planning, restoring living shorelines, DART buoys, training communities to "evacuate first, confirm later"

Flood Hazard

Extreme rainfall volume and river discharge rates over a specific return period (e.g., 1-in-20-year flood event)

Flood Exposure

Residential areas or farmland situated on active floodplains

Flood Vulnerability

Low-lying building designs, blocked drainage infrastructure, or lack of localized warning alerts

Flood Control/Reduction

Building levees/dams, elevating housing structures, and restricting floodplain development

Bushfire Hazard

Fire intensity, fuel accumulation, high ambient temperatures, and strong winds

Bushfire Exposure

Communities living along the bushland-urban interface

Bushfire Vulnerability

Flammable building materials, lack of defensible space around structures, and unmanaged fuel loads

Bushfire Control/Reduction

Managing fuel accumulation through cultural burning or prescribed burns, establishing defensible space, robust community evacuation plans

What is the Sendai Framework?

International platform guiding disaster management away from reactive emergency response toward proactive disaster risk reduction;

objective is to reduce disaster risk, protect life and property, and build resilient communities

Physical mechanism of an earthquake (elastic rebound)

Rock fracturing along faults releases stored elastic strain energy

as plates move, locked faults accumulate strain; when stress exceeds rock/frictional strength, the fault ruptures and rocks snap back into place

Hypocenter vs. Epicenter

Hypocenter (focus) = 3D underground location where rupture begins;

Epicenter = point on Earth's surface directly above it

Rupture geometry & slip

Fault ruptures extend across subsurface length and width;

strongest ground shaking and peak energy release occur where fault slip is highest, which does not always coincide with the epicenter

Richter Scale (ML)

Measures peak ground motion wave amplitude on a seismogram; effective for small-to-moderate events but saturates for larger earthquakes (ML > 6.5)

Moment Magnitude (Mw)

Measures total energy release based on seismic moment M₀ = μAd (μ = rock rigidity, A = rupture area, d = average slip displacement); each unit increase ≈ 32-fold energy increase

Gutenberg-Richter relationship

For every 1-unit step down in magnitude, earthquake frequency increases ~10 times; globally ~1 M8+/year, ~15 M7–7.9, ~134 M6–6.9; demonstrates fractal scaling; fundamental for seismic hazard modeling

What is PAGER?

Automated system estimating human and economic impacts of major earthquakes worldwide within minutes of an event

PAGER alert levels (colors)

Green: Low impact (0 fatalities, <$1M USD);

Yellow: Regional impact (1–100 fatalities, $1M–$100M);

Orange: Significant impact (100–1,000 fatalities, $100M–$1B); Red: Severe catastrophe (>1,000 fatalities, >$1B)

PAGER fatality and economic loss histograms

Probabilistic bar charts displaying statistical likelihood of different ranges of fatalities and financial damage

PAGER Shaking Exposure Table

Breaks down estimated population exposed to each shaking intensity level on the Modified Mercalli Intensity (MMI) scale

PAGER structural vulnerability & secondary hazards assessment

Assesses regional building vulnerability (e.g., unreinforced masonry) and flags potential secondary hazards like earthquake-induced landslides or liquefaction

Sea level rise (coastal hazard driver)

Long-term global climate changes that alter ocean water volume and land elevation

Storm surge causes and proportions

Abnormal rise in sea level from atmospheric pressure drops (inverted barometer effect, ~5%) and intense onshore winds pushing surface water inland (~95%) during cyclones/severe coastal storms

Coastal erosion and its drivers

Physical transport and removal of sand or rock from a beach/dune profile; driven by wave energy, tidal currents, sea level elevation, and sub-aerial weathering

Tsunami cause (coastal zone)

High-speed, long-period ocean waves triggered primarily by sudden vertical seafloor displacement during subduction zone megathrust earthquakes

Coastal zone / active profile

Dynamic interface where land, wind, waves, and sediment interact;

human development directly on the active beach profile significantly elevates exposure and vulnerability

Hydrodynamic vs. morphological coastal drivers

Hydrodynamic: significant wave height (H), wave period, storm duration, tidal stage.

Morphological: dune height/width, beach width, geology (hard rock vs. soft cliff), condition of existing engineering structures

Why is coastal exposure exceptionally high?

Three-quarters of global megacities are coastal

Eustatic sea level rise mechanisms

(1) Thermal expansion — seawater expands as oceans warm;

(2) Ice melting — glaciers, ice caps, polar ice sheets (Greenland, Antarctica) add mass to ocean basins

Isostatic / Relative sea level rise

Local land movement: land subsidence from groundwater extraction or sediment compaction (e.g., Mekong Delta), or post-glacial land adjustments

Current sea level rise trends

Accelerating from ~1.4 mm/year (1901–1990) to over 3.6 mm/year in recent decades

Average Recurrence Interval (ARI)

Statistical average time interval between extreme events of a given magnitude (e.g., 1-in-100-year storm flood)

Exceedance Probability

Statistical likelihood (P) that a specific wave height (Hs) will be equaled or exceeded during a given period

Directional Wave Analysis

Accounting for wave approach angle (directional ARI) substantially improves erosion predictions vs. non-directional models; unusual storm angles can cause severe localized erosion even with lower wave heights

Palaeo-records (palaeotsunami/geological data)

Short instrumental records miss rare extreme low-probability events; studying palaeotsunami sand sheets and sediment coring extends historical baselines by centuries to millennia, verifying models and revealing actual recurrence patterns

How climate change exacerbates coastal hazards (4 ways)

(1) Elevated base sea level enables surges/tides to penetrate further inland;

(2) Increased frequency of extreme inundation;

(3) Storm intensity — warmer SSTs drive stronger winds, higher waves, larger surges;

(4) Compounded threats to vulnerable geographies (Torres Strait Islands — risks to human rights, culture, freshwater)

Planned/Managed Retreat

Gradually rezoning land and relocating infrastructure inland to allow space for natural coastal processes to adjust over time

Beach Nourishment

Depositing sand to widen beaches; preserves natural amenity but requires continuous maintenance

Dune Revegetation

Planting native dune flora to trap windblown sand and stabilize foredunes

Living Shorelines

Restoring natural buffers (mangroves, saltmarshes, seagrass, oyster reefs) to dissipate wave energy and stabilize sediment while offering ecological co-benefits

Seawalls & Rock Armour — pros and cons

Rigid defense for critical high-value assets; expensive and often cause wave reflection, toe scour, and downdrift beach narrowing

Groynes — pros and cons

Trap sand along longshore drift to build up local beaches; starve beaches further downdrift

Hybrid Approaches

Combining hard structures with soft, ecological buffers — often delivers the most balanced resilience against changing wave climates and rising seas

Wind waves vs. tsunami waves generation

Wind waves: friction from wind blowing across water surface (fetch); disturb only upper ocean layer, orbital motion decays exponentially with depth.

Tsunami waves: sudden displacement of entire water column, commonly from subduction zone megathrust earthquakes, underwater landslides, or volcanic eruptions

Tsunami deep ocean propagation

Series of waves with long periods and extremely long wavelengths (hundreds of km); travel at jet-plane speeds (600–800 km/h) with small amplitudes (rarely >1 m) — virtually imperceptible to ships

Tsunami shoaling & amplification

As tsunami enters shallow coastal water, friction with seafloor slows it (to ~30–50 km/h); shortening wavelength forces kinetic energy upward, causing wave heights to grow significantly (amplification) and currents to intensify

Inundation vs. Runup

Inundation = horizontal distance tsunami reaches inland;

Runup = vertical height achieved above mean sea level

Tsunami primary and secondary triggers

Primary: seafloor uplift or downdrop during megathrust earthquakes at convergent plate boundaries (vast majority).

Secondary: terrestrial/submarine landslides, volcanic collapse/explosions, gas hydrate releases, meteorite impacts

Tsunami natural warning signs

(1) Strong or long ground shaking — immediate primary warning;

(2) Ocean drawback/drawdown — sea rapidly recedes exposing normally submerged ocean floor;

(3) Acoustic & visual indicators — loud roaring like freight train/jet engine, or approaching wall of foaming water

Why palaeotsunami deposits are important

Historical/instrumental records too short for rare high-magnitude low-probability events; palaeotsunami research extends disaster timelines by centuries/millennia, providing recurrence interval and size data, validating numerical models, informing long-term coastal hazard zoning

Methods and diagnostic features identifying palaeotsunami layers

Methods: trenching, sediment coring, lab analyses.

Features: sharp erosional basal contact (scour into pre-existing soil/dune); extensive sand sheets thinning/fining landward; high-energy marine sediment in low-energy/terrestrial environments; rip-up clasts; mud drapes separating wave pulses/swash-backwash cycles; marine diatoms/foraminifera in non-marine settings; evidence of co-seismic land subsidence (buried topsoil, drowned trees)

Simeulue Island (Smong)

Islanders passed down songs/lullabies about the 1907 tsunami teaching that severe shaking + sea recession required immediate fleeing to high ground (Smong); in 2004 they recognized signs and evacuated within 8 minutes — fewer than 10 fatalities out of ~78,000

Moken People (Laboon)

Sea-nomadic people of the Andaman Sea with oral stories of laboon ("the wave that eats people"); recognizing rapid ocean drawdown in 2004 as the laboon sign, they fled to high ground with almost no casualties vs. surrounding villages

Japanese Tsunami Stones

Ancestral stone markers along Japan's coast (e.g., Aneyoshi) bore warnings like "Do not build your homes below this point!" — protecting villages that heeded them during the 2011 Tohoku event

Historical evolution of tsunami warning systems

1949: first Pacific-wide system (Seismic Sea Wave Warning System) after 1946 Aleutian tsunami killed 159 in Hawaii;

1965: UNESCO's IOC founded PTWS after 1960 Chile earthquake;

2004 Indian Ocean disaster prompted regional expansions (Joint Australian Tsunami Warning System)

Three operational tools of tsunami warning systems

(1) Seismic networks — detect/locate undersea earthquakes within minutes, determine magnitude and rupture depth;

(2) DART buoys — seafloor pressure sensors linked to surface buoys measure real-time sea surface changes to confirm wave generation;

(3) Forecast modeling & alerts — numerical models project wave arrival times/heights, issuing tiered alerts (Warning, Advisory, Watch, Information Statement)

Limitations & human factors of tsunami warnings

Overreliance on engineering: hard infrastructure induces false security — 2011 Japan's 12-m seawalls overtopped by 40-m waves.

Self-reliance mindset: technical warnings can be delayed/fail; public education must emphasize rapid self-evacuation ("evacuate first, confirm later") upon feeling shaking or seeing drawdown

Volcanoes at convergent plate boundaries (subduction zones)

Where an oceanic plate dives beneath an overriding oceanic/continental plate (Pacific Ring of Fire, Cascade Range, Aleutian Arc);

water in marine sediment released into hot mantle lowers melting point (flux melting), forming explosive stratovolcanoes

Volcanoes at divergent plate boundaries

Where plates pull apart — Mid-Ocean Ridge system (Mid-Atlantic Ridge) or continental rift zones (East African Rift); upwelling mantle experiences decompression melting, producing vast underwater basaltic lava flows and new ocean floor

Intraplate hotspot volcanoes

Far from plate boundaries over stationary mantle plumes of unusually hot rock (Hawaii, Yellowstone, Galapagos); as the plate moves over the stationary hotspot, it creates a linear chain of volcanoes increasing in age away from the active vent

Basalt magma properties

Low silica, high temperature, low viscosity, low gas content, gentle flow

Andesite magma properties

Moderate silica, moderate temperature, moderate viscosity, moderate gas, moderate explosion

Dacite magma properties

High silica, low-moderate temperature, high viscosity, high gas, large explosion

Rhyolite magma properties

Very high silica, low temperature, very high viscosity, high gas, cataclysmic explosion

Seismic monitoring of volcanoes (VT vs. LP)

Volcano-Tectonic (VT) earthquakes: high-frequency, from rock fracturing as magma forces open conduits.

Long-Period (LP) events & harmonic tremor: continuous low-frequency vibrations from resonance of fluids rushing through fractures; sudden shift to harmonic tremor indicates imminent eruption

Ground deformation monitoring of volcanoes

Tiltmeters & high-precision GPS measure sub-millimeter slope/elevation changes as magma inflates or deflates the edifice;

InSAR (satellite radar) compares radar passes over time to map ground movement across entire volcanic complexes

Gas geochemistry monitoring of volcanoes

Tracks emission rates/ratios of SO₂, CO₂, and water vapor using UV cameras, DOAS, FTIR spectrometers; rapidly rising SO₂ signals shallow, ascending magma

Thermal & hydrological monitoring of volcanoes

Satellite/drone thermal infrared imaging detects heat anomalies at vents/crater lakes; changes in crater lake levels, temperature, or chemistry indicate rising hydrothermal activity

Hawaiian & Icelandic eruptions (VEI 0–1)

Non-explosive, fluid basaltic eruptions: fire fountains, long lava flows, fissure eruptions

Strombolian eruptions (VEI 1–2)

Mildly explosive bursts of lava clots, incandescent scoria, and bombs ejected tens to hundreds of meters, creating scoria/cinder cones

Vulcanian eruptions (VEI 2–3)

Short, violent, cannon-like explosions from gas buildup beneath a hardened crust/lava plug; releases dense ash plumes and blocks

Pelean eruptions (VEI 3–4)

Explosive collapse of viscous lava domes generating deadly, high-speed pyroclastic flows (glowing clouds of superheated gas and ash)

Plinian & Ultra-Plinian eruptions (VEI 5–8)

Cataclysmic explosions with sustained towering eruption columns reaching 20–50+ km into the stratosphere, blanketed ash falls, widespread pyroclastic flows, caldera collapse (Vesuvius 79 AD, Mt. St. Helens 1980, Krakatau 1883)

Phreatic eruptions

Steam-driven: groundwater superheated by underlying magma (without direct contact) causes sudden steam explosions blasting out pulverized pre-existing rock, no new magma

Phreatomagmatic / Surtseyan eruptions

Ascending magma directly encounters water (ocean, lake, aquifer), causing explosive steam expansion, fine ash generation, and surge deposits (Surtsey 1963, Hunga Tonga-Hunga Ha'apai 2022)

How fire differs across space

Fire activity varies across global pyromes and regional pyrogenics, shaped by climate domains, vegetation/fuel types, productivity/aridity gradients, and human ignition patterns; highly productive wet forests burn infrequently but with extreme intensity; dry savannas burn frequently with lower intensity

How fire has differed across time in Australia

Pre-colonization (~1788): Indigenous stewardship maintained low fuel loads and open grassy woodlands.

Post-invasion: dispossession/massacres disrupted cultural burning → vegetation thickening, "eucalypt explosion," fuel load rise.

Modern amplification: anthropogenic climate change since ~1950 layered higher temperatures/drier conditions onto heavy fuel loads → catastrophic megafires

Scientific proxies/evidence for historical fire

Palaeoecology & sediment coring (Lake Elusive, Purghagoolah on Gunaikurnai Country) with radiocarbon and Pb²¹⁰ dating;

Charcoal morphology (blocky = high-temperature woody/canopy fires, elongated = cooler grass fires);

pollen analysis tracks vegetation shifts;

dendrochronology (tree rings, fire scars) reveals exact fire years/frequency;

historical art & maps (Mount Gambier, Budj Bim) document open park-like landscapes;

satellite/remote sensing (NASA FIRMS) tracks active hotspots, emissions, global burn extent

Risks posed by fire

Human & economic: threat to life, home destruction, livestock loss, air pollution/smoke taint impacting health and agriculture.

Ecological: severe soil erosion, nutrient loss, destroyed habitats, massive CO₂ emissions undermining carbon offset markets

Fire risk equation

RISK = Likelihood × Consequence;

risk reduction focuses on lowering likelihood of ignition/spread or reducing consequences to critical assets

How fire can be suppressed

By removing oxygen (smothering), reducing temperature (water), or removing fuel (dozer lines, rake-hoe lines)

Operational triaging by fireline intensity (kW/m)

<800: controllable directly with hand tools and water support;

<2,000: direct attacks possible with heavy machinery, tankers, water bombers;

<3,000: requires indirect attacks using machinery and tankers;

>3,000 (up to 10,000+): unlikely to be suppressed, exceeds human control capacity

Four prescribed burn zones

(1) Asset Protection Zone (APZ): directly adjacent to infrastructure to minimize flame contact;

(2) Bushfire Moderation Zone (BMZ): strategic buffer zones around townships;

(3) Landscape Management Zone (LMZ): broader landscape burning for ecosystem health;

(4) Planned Burning Exclusion Zone (PBEZ): fire-sensitive conservation areas

Tolerable Fire Interval (TFI) trade-off

In Victoria, ~50% of prescribed burns fall below the minimum TFI — a policy triage decision to risk long-term vegetation regeneration in order to protect human life and property

What is a fire regime?

The overarching pattern of fire in each ecosystem over time, defined by frequency, intensity, severity, seasonality, fuel type, and spatial extent

Three multi-scale fire triangles

Basic Fire Triangle: Heat, Fuel, Oxygen.

Fire Behavior Triangle: Weather, Topography, Fuel.

Fire Regime Triangle: Climate, Ignitions, Vegetation/Fuel

Why fire regimes are useful

Let scientists classify ecosystems into global pyromes and regional pyrogenics to predict fire behavior; help land managers identify whether a landscape is driven primarily by climate/weather or fuel accumulation, guiding intervention strategies

Fire Intensity vs. Fire Severity

Intensity = rate of heat energy released during combustion (fireline intensity in kW/m, governed by rate of spread, flame height/length, fuel consumption).

Severity = immediate physical/ecological impact or damage left behind (depth of organic soil loss, canopy scorch, defoliation). Intensity measures energy output during fire; severity measures environmental impact after fire

What is Cultural Burning?

A sophisticated First Nations land stewardship practice involving frequent, cool, low-intensity, highly targeted burns across small patches of Country