Natural Hazards Exam 1

Hazard

A natural event that has the potential to cause harm or damage (e.g., a volcano in an uninhabited area).

Disaster

A natural event that causes significant loss of life and property damage that exceeds a community's ability to cope.

Catastrophe

A massive disaster requiring massive amounts of time and money to recover from.

Mitigation

Actions taken before an event to reduce long-term risk (e.g., building sea walls, strict building codes).

Preparedness

Planning and educating before an event (e.g., evacuation drills, emergency kits).

Emergency Response

Immediate actions during/after an event to save lives (e.g., search and rescue, medical care).

Recovery

Rebuilding and restoring community operations long-term after an event.

Crust

Thin, outermost rocky layer (Continental is thick/granite; Oceanic is thin/basalt).

Mantle

Thick middle layer made of solid to semi-molten rock (peridotite)

Lithosphere

Rigid outer shell combining the crust and uppermost solid mantle.

Asthenosphere

Weak, ductile layer of the upper mantle where plates slide.

Core

Innermost metallic layer (Liquid Outer Core creates magnetic field; Solid Inner Core).

Divergent Boundary

Plates move apart (Creates mid-ocean ridges, rift valleys; Example: Mid-Atlantic Ridge).

Convergent Boundary

Plates move together (Creates subduction zones, deep trenches, mountain ranges; Example: Cascades, Himalayas)

Transform Boundary

Plates slide past each other horizontally (Creates strike-slip faults; Example: San Andreas Fault).

Fault

A fracture in rock along which movement has occurred.

Hypocenter (Focus)

The exact location underground where rock ruptures and earthquake energy releases.

Epicenter

The point on Earth's surface directly above the hypocenter.

P-Waves (Primary)

Fastest body waves; push-pull compressional motion; travels through solids and liquids.

S-Waves (Secondary)

Slower body waves; side-to-side shear motion; travels ONLY through solids

Triangulation

Method using S-P lag times from at least 3 seismograph stations to locate an epicenter.

Magnitude

Quantitative measurement of energy released (e.g., Moment Magnitude Scale).

Intensity

Qualitative measurement of ground shaking and damage impact on humans (e.g., Modified Mercalli Scale).

Liquefaction

Process where water-saturated loose soil behaves like a liquid during strong shaking.

1964 Alaska Earthquake

Megathrust subduction quake (M_w 9.2); triggered huge tsunamis and massive landslides.

2010 Haiti Earthquake

Strike-slip fault quake (M_w 7.0); massive catastrophe due to poorly constructed buildings and weak infrastructure.

2011 Japan (Tohoku) Earthquake

Megathrust subduction quake (M_w 9.1); caused a devastating tsunami and Fukushima nuclear meltdown.

Viscosity

Resistance to flow (High = thick/sticky, Low = runny).

Volatiles

Dissolved gas content (High gas = explosive power).

Volume

Total amount of magma erupted.

Shield Volcano

Broad, gently sloping cone built from low-viscosity basaltic lava flows (e.g., Mauna Loa).

Stratovolcano

Tall, steep cone built of alternating lava and ash; explosive (e.g., Mt. St. Helens).

Cinder Cone

Small, steep hill formed from loose pyroclastic debris thrown out during single eruptions.

Pyroclastic Flow

High-speed avalanche of superheated gas, ash, and rock fragments—the deadliest volcanic hazard.

Lahar

Volcanic mudflow formed when ash mixes with melting ice, snow, or heavy rain.

Volcanic Explosivity Index

Relative scale ranking eruption size based on erupted volume and plume height.

1980 Mt. St. Helens

Cascade stratovolcano; lateral blast triggered by a massive landslide.

79 AD Mt. Vesuvius

Eruption buried Pompeii in ash and Herculaneum in hot pyroclastic surges; evidence preserved in plaster casts.

1630 BC Santorini (Thera)

Massive Minoan eruption that collapsed an island caldera and produced severe tsunamis in the Aegean Sea.

Mass Movement

The downhill movement of soil, rock, or debris under the direct force of gravity.

Slope Failure Factors

Excess water, steep slope angle, weak rock layers, loss of vegetation, human undercut.

Creep

Extremely slow, gradual downhill movement of soil indicated by curved tree trunks and tilted fences.

Rockfall

Free-falling rocks detaching from steep cliffs at high speeds.

Debris Flow / Mudflow

Fast-moving fluid mixture of mud, water, rock, and debris down channels.

Rotational Slide (Slump)

Mass moves along a curved concaved surface, tilting backwards.

Translational Slide

Mass slides along a flat, planar surface of weakness.

Landslide Mitigation Structures

Retaining walls, shotcrete, rock bolts, benching, terrace drains, and debris basins.

Snow Avalanche

Fast downslope movement of snowpack; survival relies heavily on wearing an avalanche beacon, probing, and shoveling within the first 15 minutes.