Natural Hazards & Disasters exam 2

Tsunami

a rapidly moving, long-wavelength ocean wave generated by displacing ocean water.

Amplification

When tsunami wave height increases in shallow water.

Run-up

Maximum wave height of the tsunami when it hits shore, with respect to sea level.

Local tsunami

When an earth process (like earthquake or landslide) occurs locally and produces a tsunami that hits the coast within a short time (ie. within minutes).

Distant tsunami

When a earth process (like an earthquake or landslide) produces a tsunami that travels a long distance (ie. 100s of km) and for a long time (ie. hours) before hitting a distant coast.

Magma

A combination of crystals, melted rock, and dissolved gas, that occur in isolated chambers within the crust and the upper most mantle.

Lava

Magma erupted at the earth’s surface.

Decompression Melting

A method of creating magma in which the pressure decreases while the temperature stays constant and hot.

Mafic (basaltic)

A category of magma characterized by its iron- & magnesium- rich chemical composition.

Forms basalt.

Felsic (rhyolitic)

A category of magma characterized by its silicon, aluminum, potassium, and sodium-rich chemical composition.

Forms rhyolite.

Intermediate (andesitic)

A category of magma with a composition between that of Mafic and Felsic.

Forms andesite.

Viscosity

A substances (in this case, primarily magma’s) resistance to flow.

Crater

A depression that forms as erupted pyroclastic debris accumulates around vent.

Caldera

Large depression forms after a volcanic eruption, when the roof of a magma chamber collapses over the partially-emptied magma chamber.

Pyroclastic Flow

A dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases that is blasted out of a volcano and rapidly travels downhill.

Lahar

Volcanic activity-related mudflow/debris flow that can occur with or without a volcanic eruption. Lahars are associated with volcanoes because of the internal heat, but they don’t need an eruption to occur.

Stream Gradient

The slope of a stream channel (vertical drop/horizontal distance).

Base Level

The lowest elevation a stream can erode down to.

Long Profile

Changes in a stream’s elevation from its headwaters to its mouth.

Flood

When water flows outside the banks of a stream’s channel.

Stage

The height of water in a river.

Discharge

The quantity of water flowing past certain points on a stream (volume/time) that is calculated using the measured depth (stage) and flow velocity, and a known channel width.

Recurrence Interval

(R) is a probability expression, and the average time between events. Calculated by R = (N+1)/M, where M is the magnitude and an M=1 is the highest flow.

Triggers of tsunamis, include:

earthquakes, landslides, volcanic eruptions, and meteorite impacts

Characteristics of tsunami waves:

1. long wavelength waves that can travel fast and far

2. wave height increases (amplification) in shallow water

3. a tsunami generated offshore can cause both a distant tsunami and local tsunami.

How was the Indonesian Tsunami (2004), aka the Indian Ocean Tsunami triggered?

It was triggered by a Magnitude 9.0 earthquake at an oceanic-oceanic convergent plate boundary tectonic setting (subduction zone).

Primary effects of tsunamis include:

Flooding, eriosion, debris, vegetation removal, subsidence, etc.

Secondary effects of tsunamis include:

fire, water contamination, and disease outbreaks.

Examples of how humans can minimize the consequences of tsunamis.

1. installing tsunami warning systems

2. using science-informed land-use planning and civil engineering to minimize human development and therefore loss of life and property damages in tsunami “run-up” zones.

3. Increasing public awareness of the tsunami hazards and ecavuation/emergency procedures.

What makes up a tsunami warning system?

A network of tidal gauges, seafloor tsunameters, and seismograph stations.

Where, generally, does volcanic activity occur? give an example of each

Divergent plate boundaries, at mid-ocean ridges and rift valleys (ie. Iceland)

Convergent plate boundaries with subduction of oceanic lithosphere (ie. Japan)

Intra-plate hotspots (ie. Hawaii)

The three ways to melt hot rock

1. Increase pressure at a constant, low pressure (ie. at hotspots)

2. Decrease pressure at a constant, high pressure (decompression melting) (ie., at divergent boundaries)

3. Add dissolved volatiles (like water) to magma (ie. at convergent plate boundaries with subduction).

What controls magma’s viscosity?

1. the temperature of the magma (hotter magma has lower viscosity)

2. the composition of the magma (more mafic = lower viscosity; more feltic = higher viscosity)

What controls the type and shape of a volcanic eruption?

• Magma’s viscosity

• Magma’s volatile content

The three volcanic types with descriptions and example.

1. Shield volcano — large, broad, arch-shaped volcano with effusive eruptions fed by low-viscosity, low-volatile-content, mafic magma (ie., Hawaii)

2. Stratovolcano (aka pyroclastic) — large, steep-sided, cone-shaped volcano with alternating effusive AND explosive eruptions fed by higher-viscosity, intermediate magma (ie., Mt. Fuji)

3. Continental caldera — a large depression associated with volcanic activity that forms from a catastrophic eruption involving the collapse of a partially emptied magma chamber that is fed by high-viscosity, high-volatile-content, felsic magma (ie., Yellowstone)

Examples of geothermal features that are related to volcanic activity

Hot springs and geysers (ie. Yellowstone)

Examples of volcanic hazards

Lava flows and lava tubes, pyroclastic debris, pyroclastic flows, lahars, landslides, tsunamis, poisonous gases, fires, crop failure, famine, global climatic cooling, and aviation hazards.

What can pyroclastic flow result from?

1. eruption column collapse

2. lateral blasts

3. lava dome collapse

What approaches can humans take to minimize the loss of life and property due to volcanic activity?

• using the geologic record to understand a volcano’s eruption history (frequency, extent of deposits, and explosiveness of eruptions)

• monitoring for warning signs to help predict an imminent volcanic eruption including

• using civil engineering and community planning to minimize consequences

• using warning and communication systems to communicate volcanic hazards

examples of warning signs that humans can use to predict an imminent volcanic eruption:

Earthquakes, changes in temperature and flow of groundwater and surface water, changes in the elevtation and slope of the land surface, changes in the magnetic properties of rock, an increase in volcanic gas emmissions

Examples of civil engineering and community planning to minimize conseuences of volcanic activity:

Installing lahar sensors, lahar diversion channels and levees, and community emergency preparedness/evacuation plans.

Name the three zones of a river system

Zone 1: The “Zone of Production”

Zone 2: The “Zone of Transport”

Zone 3: The “Zone of Deposition”

Provide the following about Zone 1: location, channel slope, river floodplain and valley characteristics, water velocity, geologic processes, and types of flooding that occur here.

High elevation, high gradient, steep-sided, v-shaped valleys, tributaries that feed into main channel,

Geological processes — vertical erosion (down-cutting), production of sediment by erosion.

Types of flooding — flash flooding.