Terms in this set (100)
What Fuels Natural Disasters?
1. Extraterrestrial impacts 2. Gravity
3. Earth's internal heat
4. The Sun
is due to heat release from Earth's residual internal energy.
3 Main Rock Types
Igneous rocks: crystallizabon from molten material
Sedimentary rocks: deposition of material at Earth's surface
Metamorphic rocks: solid-state changes due to heat and/or pressure
The way these rocks 'change' into one another
form from the crystallization of molten material.
on the surface
in Earth's crust
Igneous rocks are classified according to:
is a function of cooling rate
Intrusive igneous rocks
a.k.a. plutonic rocks form from the slow crystallization of magma at depth = coarser-grained interlocking
Extrusive igneous rocks
a.k.a. volcanic rocks form from the fast crystallization of lava on the surface = finer-grained interlocking texture.
a naturally occurring solid inorganic element or compound having an orderly internal structure, a characteristic chemical composition, crystal form, and physical properties.
Common elements in crust
Oxygen (O-2) 45.20%
Silicon (Si+4) 27.20
are the most abundant on Earth!
Intermediate composition rocks
are dark and light colored.
are light colored.
How Do Volcanoes Form?
Form when magma, created by the melting of pre-existing rock, reaches the surface through fractures and extrudes as lava.
Explosivity is determined by
1. Volatiles (gas): 1-6% (may be up to 10%) Primarily H2O(g) and CO2
2. Viscosity: the resistance to flow
Factors Influencing Viscosity
1. Composition: increase silica content = increase viscosity
4 types of magma/lava classified by their mineral assemblages (amount of Si-O).
2. Temperature: increase heat = decrease viscosity
Si-O bonds form, making the magma stickier and thicker as it cools.
Highly viscous magmas/lavas with greater amounts of volatiles
Low viscosity magmas/lavas with smaller amounts of volatiles
Anatomy of an Eruption
1. Magma forms in the crust (melting of pre-existing rock)
2. Gas is dissolved in magma because of high pressures
3. Magma rises through crust due to density differences
4. Gas bubbles begin to form due to lower pressures (vesiculabon)
5. Viscous magmas trap gas bubbles = pressure build up = explosive volcanism (bubbles ≥ 75% by volume)
5. Non-viscous magmas allow gas to escape = nonexplosive volcanism
molten material that solidifies on Earth's surface
molten material that cools rapidly at the Earth's so that crystallization does not occur
Pyroclastic ('fire fragments') debris
material that is ejected during an eruption (ash size to house size)
compounds that bubble out of a magma/lava in gaseous form
is intermediate to felsic
ultramafic (<45% silica)
Divergent Plate Boundaries
Crust is extended (tension) & new crust is created.
A continental rift zone can develop into an oceanic rift
zone through time, eventually intruding/extruding mafic magmas/ lavas = new oceanic crust.
(a decrease in pressure with no change in temperature lowers the melting point of the mantle rocks) = generation of magma/lava = volcanism.
Pressure increases with depth.
Increase pressure = an increase of a mineral's mel9ng point (pressure cooker).
Sea Floor Spreading
occurs when oceanic lithosphere is pulled apart at the mid-oceanic ridges and new (mafic) molten material crystallizes in place. The sea floor moves apart from both sides of the ridge towards deep sea trenches where it is subducted.
East African Ria Zone
In 2002, low viscosity ultramafic lava (SiO2 = 42%) moving up to 60 mi/h killed >100, destroyed 25% of the buildings in Goma, popula9on 500,000.
Thermal mantle plumes origina9ng at the outer-core/mantle boundary that par9ally melt the solid mantle and overlying lithosphere (oceanic or con9nental) = volcanism
Hot Spot Volcanism: Hawaiian Islands
Oceanic crust + Mantle = Non-explosive volcanism
MAFIC + ULTRA MAFIC =MAFIC
Low silica,Low viscosity, Dark color rocks basalts/gabbros
Convergent Plate Boundaries with
As the oceanic lithosphere subducts, it heats up and dehydrates. Volatiles (water) migrate into the overlying mantle & lower the melting temperature = magma production.
Magma rises through the lithosphere due to density differences = volcanism
are curving chains (arcs) of active volcanoes that denote subduction zones
The "Pacific Ring of Fire" is a result of plate subduction
Continental Volcanic Arc: The Cascades and Coast Mountains
The Cascadia subduction zone = active volcanism (past 2 Ma) due to the subduction of the Juan de Fuca Plate under the North American Plate.
mountain that forms as a result of volcanic activity
a steep- walled, bowl-shaped depression surrounding the volcanic vent where volcanic material erupts from.
Volcanic Explosivity Index (VEI) created in 1983
1. Volume of material erupted
2. Height of the eruption column 3. Duration of the eruptive blast
Composed of many mafic, low viscosity lava flows with <1 wt. % volatiles.
Very large and gently sloping (like a warrior's shield).
1. Fissure eruptions of hot, low viscosity basaltic lava where volatiles escape easily = lava fountains.
2. Formation of spatter cones as blebs of lava collect around a vent or fissure.
3. After initial degassing, great volumes of basalt flow out of fissures
A conical hill formed by the accumulation of mafic to intermediate silica content pyroclastic material (cinders 4-32 mm) and lava around a volcanic vent.
Small (<1500 e high), steep sided (30-40 degree slopes), easily eroded.
1. Mafic to intermediate silica composition, medium to high volatile content = short-lived, small volume explosive outbursts of pyroclastic material.
2. Degassed lava flows from under the cone or ponds in the vent to create a lava lake.
a.k.a. stratovolcanoes: composed of alternating layers of intermediate to felsic lava and pyroclastic material = moderately steep slopes.
Tall, conical, glacier-covered.
Intermediate to felsic, high volatile content = relatively short-lived but powerful eruptions rising several km into the atmosphere traveling at 100's of m/sec, resulting in a moderate dispersal area.
Can result from the depressurization of the entire volcano (rupture of the lava dome) and can signal the first "throat clearing" stage of a large eruption.
Creates moderate amounts of tephra (airborne fragmental material) and pyroclas2c flows.
Intermediate to felsic, high volatile content = voluminous, sustained ejection of pyroclastic material up to 50 km (30 mi) into the atmosphere at 100's m/sec, resulting in a very broad dispersal area (100's-1000's km).
Can be the final phase of a major eruption.
Creates large amounts of tephra (airborne fragmental material) as well as pyroclastic flows, and lahars
can reach altitudes of 50 km (30 mi), allowing ash to travel around the globe depending on prevailing winds.
Create own weather (rain and lightening).
forms from small amounts of viscous, felsic, low volatile lava extruding after the main eruption above the vent and inside the crater. Often after degassing from Vulcanian/Plinian-style eruptions.
large depressions (2-75 km in diameter) caused by the inward collapse of overlying rock into an evacuated magma chamber.
Caldera: Crater Lake, OR
Formed after large Vulcanian and Plinian-type eruption phases of a stratovolcano (Mt. Mazama), characterized by a voluminous, felsic, high-volatile eruption.
depend on materials extruded which dictates the eruption style (silica content, temperature, volatiles by wt. %, and volume of material ejected).
Low viscosity lavas in Hawaiian-type eruptions are greatest lava threat because can flow quickly and spread laterally.
Ash-pyroclastic Material (Tephra)
pyroclasts smaller than 2 mm in diameter.
Volcanic bomb-pyroclastic Material (Tephra)
tephra >64 mm (2.5 in) that's erupted in a molten state and then cools in the air/on the ground.
fragment >64 mm (2.5 in) erupted in a solid condition. Composed of material from previous eruptions.
are lateral flows of a turbulent mixture of hot gases and pyroclastic material (volcanic fragments, crystals, ash, pumice, and volcanic glass shards) common in Vulcanian/Plinian-style eruptions.
Flow direction is partially dictated by topography. Has ramifications for development on the flanks of stratovolcanoes.
Lahars (volcanic mud flows)
mixture of water, volcanic ash, and debris.
Travel up to 65 km/hour (40 mph).
Huge erosive power.
Usually follow rivers and can travel substantial distance.
can cause extensive damage and are disastrous because:
1. Can travel long distances.
2. Can occur as a primary effect during an eruption or a secondary effect long aver an eruption with very little warning!
VOG volcanic smog
can aggravate respiratory issues.
Can leech lead from nails and paint; may be hazardous if drinking water is from rooftop catchment tanks. Can destroy crops
GOALS: to decrease loss of life, property damage, and disrupKon to society and economy.
Ways to predict eruptions
1. Collect data on eruptive history (type & frequency). 2. Create a hazards map based on past history.
3. Begin a monitoring scheme.
Eruption Prediction: Collecting Data
1a. Compile existing data.
Pyroclastic flow deposits
1b. Conduct geological mapping: examine type, distribution, age of deposits from past eruptions to predict future behavior and frequency.
Geochemistry: determine silica content = explosivity. Geochronology: age of deposits/eruptions = return period.
Eruption Prediction: Create Maps
2. Identify hazards, produce a volcanic hazards
map, and determine the most likely eruption scenario.
Eruption Prediction: Monitoring
3. Install seismic stations, GSP network, and conduct water and gas sampling
1. Ground deformation
swelling or deflation of the volcano due to magma movement and changes in fluid and gas pressure.
Horizontal Displacement Measurements
Manually measure displacements
Tiltmeters: measure the change in distance between 2 points through time.
GPS (global positioning system)
pinpoints horizontal and vertical ground movements through time.
What Do We Measure or Look For?
1.Ground deformation, 2. Growth of lava dome (visible), 3. Increased seismic activity, 4. Increased gas emissions, 5. Increase in heat flow,
A. Low frequency earthquakes define the magma conduit.
B. Absence of seismic activity outlines the magma chamber.
C. High frequency earthquakes above magma chamber reflect the brille fracturing of rocks as magma intrudes.
Eruption Prediction: Monitoring
1. Install/reinforce seismic network (real-time)
2. Install/reinforce GPS network (real-time)
3. Gas emission sampling (e.g. COSPEC)
4. Measure cracks regularly
5. Chemical analysis of eruptive deposits
6. Daily observation
are regular oscillations that propagate in space
Distance from crest to crest
Doubling wavelength, doubles energy; doubling wave height quadruples energy!
Waves when talking about energy
a wave is the mechanical expression of moving energy
Amount of energy transmitted & corresponding wave height depends on
1. Wind speed
2. Wind duration
4. Original sea state
occur when many waves of different amplitude and wavelength combine constructively.
force that disturbs water (input energy)
force that causes water to return to its undisturbed state
Water rotates in place and energy propagates through (except near shore)
the bottom limit of orbital water movement = 1⁄2 the wavelength of the surface waves Wave base = L/2
Deep water wave
water depth >L/2
For L/20 < water depth < L/2, S is affected by both d and L
Shallow water wave
water depth <L/20
the wave 'feels the ocean bopom'. Velocity is determined only by depth
when the depth of water >L/2, the wave does not feel the bottom and the wave velocity (Vw) is determined only by the wavelength (L)
a change in wave characterisNcs as waves move from deep to shallow water.
When steepness ≥1/7, waves become unstable and break.
Water depth beneath a breaker is 1.3 Nmes wave height, so the water velocity in the wave crest > water velocity in the wave velocity and the crest outraces the bogom and falls forward.
Japanese word for 'harbor wave' due to shoaling. Displacement of large amounts of water in a short period of time
Tsunami caused by:
1. Volcanic eruptions
3. Meteorite impacts
(vertical submarine fault motion)
Tsunami From Earthquakes
Generated from vertical displacement on submarine faults.
Compression and catastrophic release of stress = elastic rebound.
Megathurst earthquakes at subduction zones.
Crests and troughs
The crest and troughs of a tsunami reflect the movement of the ocean floor
Tsunami height and run off
Tsunami height and run-up is an affect of bathymetry/topography and the process of shoaling.
Why are tsunami so destructive
Most destruction is not due to the height of the waves but from the momentum of the large water mass and ultra long wavelengths and periods.
It's like a rapidly rising tide or tabular sheet of water, not a curling wind wave with a steep trough behind its leading edge.
The increase in wave height can be exacerbated by local bathymetry/topography and the shape of the shoreline.
Sendi, Japan 2011
Waves can travel up rivers as well as great distances inland if the topography is flat.
Narrow streets can funnel water and increase water height above that of the highest tsunami wave.
the slowing and bending of waves in shallow water.
PrevenAon, PredicAon, Mitigation
Prevention and prediction are difficult due to the nature of and many sources of tsunami: earthquakes, volcanic eruptions, landslides, meteorite impacts.
Engineer buildings that withstand tsunami and are multistory with vertical evacuation options.
Create waterfront parks or leave low-lying coastal areas undeveloped.
Preserve coral reefs and coastal vegetation, which buffer waves.
Education and awareness.
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