Home > Flashcards > Print Preview
The flashcards below were created by user
on FreezingBlue Flashcards. What would you like to do?
Keys to protecting people and property are:
- Assessment - could it erupt? If so, how violently?
- Monitoring - watching for signs of impending eruption
- Mitigation - how to prepare for and respond to an eruption
Positive aspects of living with volcanoes
- Volcanic soils are some of the most fertile in the world.
- Snow cover on volcanoes provides summertime stream flow.
- Heat inside volcanoes can be a source of geothermal energy.
- Volcanoes are sometimes associated with deposits of gold, silver, copper, and other precious metals.
Negative aspects of living with volcanoes
- Eruptions may be violent, destroying lives, infrastructure, and natural resources.
- Effects may be widespread, especially due to ash fall.
- Airborne ash poses hazards to airplanes.
- Effects may last for years to decades because loose volcanic deposits are easily eroded and remobilized as mudflows.
The Cascade Volcanoes
- The Cascades are a volcanic mountain chain stretching from northern California to southern British Columbia.
- They are a broad (50-80 mile-wide) volcanic platform with ~16 major high (10,000-14,000 ft elevation) volcanic cones.
- All historic volcanic eruptions in the lower 48 states have been Cascade volcanoes. Baker, Rainier, and St. Helens have been the most active volcanoes in historic times.
The Cause of Cascades Volcanism
Internal Structure of Earth
- Crust (Solid & Rigid)
- Mantle (Solid but deformable)
- Outer Core (Liquid)
- Inner Core (Solid)
- Solid and Rigid
- Rich in light elements (Si, Al, K, C, O, etc.)
- Only 0–90 km thick (0–11 km for oceanic crust, 25–90 km for continental crust)
- Solid but deformable
- Mixed elements (mostly Si, O, Mg, Fe)
- From base of crust (0–90 km) to 2900 km; accounts for 2/3 of the entire mass of Earth
- Heavy, molten Fe and Ni metal. Circulation of liquid Fe creates our magnetic field.
- From 2900–5155 km deep
- Heavy, hot Fe and Ni, but the pressure is so high that is is solid.
- From 5155–6370 km deep
Where does lava come from?
- The liquid metal of the outer core is way too deep and dense to ever rise to the surface.
- Under the right conditions, parts of Earth’s solid mantle and crust can melt, creating lava that is hot enough and buoyant enough to rise to Earth’s surface.
Internal Structure Observation of Earth
- Total mass minus mass near surface leaves a lot of mass that must be hidden in its deep (dense) interior.
- Earth’s strong magnetic field requires a large body of magnetic material such as a convecting zone of liquid iron.
- Meteorites fall to Earth are pieces of planetary bodies that were once similar to Earth, but were destroyed by collisions.
- Earthquake waves that cannot travel through liquid, and they do not travel through the central part of Earth’s interior.
- The sliding plates (called “Plate Tectonics”) is one of the greatest revolutions in Earth Science
- Most earthquakes and volcanoes occur at plate boundaries.
- (Greek: Strong)
- The outer 100 km or so of Earth is a rigid, brittle shell
- The lithosphere is broken up into pieces or “plates”, like a cracked shell on a hard-boiled egg.
- (Greek: Weak)
- These plates can slide around on the underlying weak mantle
- Is solid, but deformable (like plastic)
- Greek “tecton”: builder / architect
- The study of large features on Earth’s surface and the processes that formed them.
- Large features:continents, ocean basins, mountain ranges
- Processes:earthquakes, volcanic eruptions
- Due to movement of plates ofEarth’s outer shell.
- 1912 Alfred Wegener
- Stated that there once existed a large “supercontinent” (called Pangea) that split into the pieces that are our present continents.
Wegener based his idea on 4 observations
- 1. Fit of the continents
- 2. Crust appears to “float” on the mantle
- 3. Correlation of fossils, rocks, glacial depsoits, and mountain belts
- 4. Diversity of Species
Fit of the continents
The coastlines of many of the continents appear to fit together like pieces of a jigsaw puzzle.
Crust appears to “float” on the mantle
Continental crust is thicker than oceanic crust, but most of that extra thickness is hidden below the surface as a deep “root”.
Correlation of fossils, rocks, glacial deposits, and mountain belts
Areas of specific fossils or rocks, or mountain belts, became continuous across what is now open ocean if the continents were fitted back together as their coastlines suggested.
Diveristy of Species
Animals that existed before Pangea split apart were similar between continents, whereas animals that existed after the continents separated are often unique to certain continents (such as the unusual mammals of Australia).
Wegener’s Continental Drift idea had two critical weaknesses
- No reasonable mechanism for why the continents would drift
- We knew that Earth’s crust beneath the oceans was solid rock. How could the continents possibly plow through the ocean crust as they moved around?
- (SOund Navigation And Ranging)
- During and after WWII revealed some oceans had long ridges down the middle (“mid-ocean ridges”) that looked like the rift valleys that we see on land (e.g. Iceland, Rio Grande Valley, Red Sea)
Typical Rates in Plate Tectonics
- Plates move at 1–10 cm/yr (a few inches/yr) [rate of fingernail growth]
- ~ 3-14 m in a human lifespan (70 yr) = 10-100 km/million years
- Rates confirmed over: Geologic time (magnetic stripes on seafloor), Modern times (surveys, GPS measurements)
Two Important Factors in the Development of Landscapes
- 1) Type of Plate boundary
- 2) Type of Crust
Type of Plate Boundary
- 1. Divergent
- 2. Convergent
- 3. Transform
- 4. (Hotspot)
Type of Crust
- Continental (thick; more buoyant)
- Oceanic (thin; less buoyant)
Tectonic (Lithospheric) Plate
- Continental Crust: thick and rides high
- Hard plate of Lithosphere is made of crust & uppermost mantle
- Oceanic Crust: thin and sits low
- Plates rides on softer part of mantle (Asthenosphere)
Divergent Plate Boundaries
- Plates move away from one another.
- Plates (Lithosphere) created
- Mid-Atlantic Ridge
Convergent Plate Boundaries
- Plates move toward one another.
- Plates Destroyed and Recycled
- Subduction Zone
Transform Plate Boundary
- Plates slide past one another.
- Lithosphere neither created nor destroyed.
- Pacific plate slides past the N. American plate along the San Andreas Fault in Cali.
- Plates rides over plume of hot mantle.
- Important, but not a plate boundary.
- The hawaiian Islands form as teh Pacific Plate moves northwestward over a stationary hotspot.
Three Stages of Divergent Plate Boundary Development
- Continental Rift / Mid-Ocean Ridge
- New Ocean (Red Sea)
- Mature Ocean (Indian Ocean)
Mid-Ocean Ridges Circle the Globe
- East Pacific Rise
- Mid-Atlantic Ridge
- Mid-Indian Ridge
Basin and Range Province
A continental rift zone in the western U.S. and Mexico.
San Andreas Fault
- Pacific Plate and Norht American Plate
- Transform Palte boundary is a broad zone of shearing between two plates
Observations along Hawaiian Island Chain
- Islands are older in a norhtwest direction.
- Islands are more eroded in a northwest direction.
- Islands are shorter in a northwest direction.
- Yellowstone National Park, Wyoming
- Geothermal features form due to regions lies about the Yellowstone hotspot
Formed as a plate capped with oceanic crust plunges down at a subduction zone.
Subducting Juan de Fuca Plate froms two Parallel mountain ranes in the Pacific Northwest
- Oceanic sediment and basalt scraped off subducting plate, forming Coastal Mountains.
- Subducting plate dehydrates, forming Cascade Volcanoes.
- Puget Sound and the Willamette Valley are low-lying regions between the rising mountains.
- In OR and WA, subduction causes two different mountain ranges.
- The Coastal Ranges contain materials that were manufactured in the sea, then scraped off the subducting Juan de Fuca Plate
Layers lifted out of the Sea.
- Lava erupts into cold ocean water
- Lava squeezes in tube
Why are the Cascade Volcanoes in such a straight line?
- The Cascade Volcanoes lie above the line at which the top of the Juan de Fuca plate is deep enough (~50 miles), so that it is hot enough to dehydrate (sweat)
- The Cascades are volcanoes formed above the sweating plate
Leads to the highest topography on earth.
Cascadia Subduction Zone
- Juan de Fuca Plate subducts underneath the North American Plate at ~3 cm/yr.
- At the Surface: magma reaches the surface (called lava), it erupts & forms volcanoes.
- In the Upper Crust: magma is hot enough & finds a pathway through the crust it will make it to the surface or stay in crust & cool, & not erupt. In this case it will form a large body of igneous rock called a pluton.
- In the Upper Mantle/Lower Crust: Water driven off of the descending plate migrates upwards lowering melting temperature, causes melting of the overlying mantle, forming magma that rise throught the mantle & crust.
- (fault-bounded basin)
- Separates the Western Cascades from the High Cascades.
- Provide pathways to the surface for magmas
- Helps explain the abundance of volcanism in the central Cascades of Oregon.
- The low area created by the down-dropped graben contains many lakes.
3 Ways to make rocks melt
- 1. Increase in temperature
- 2. Decrease in pressure
- 3. Addition of impurities
Melting point of rock is lower at lower pressure.
- Chain of volcanoes above a subductionzone
- = arc-shaped on a map (earth is round)
What happens when rock melt?
- Rocks are made up of minerals, and different minearls have different melting temperatures.
- Chemical composition of the partial melt depends on what minersals melted to create it.
- only part of the rock melts at any one time
- less dense than the rock it melted from, so it will start migrating upwards through the mantle.
- molten liquid
- magmas formed by between 1% and 20% partial melting of mangle rocks
magma erupts onto Earth's surface
magma solidifies underground
Extrusive (Volcanic Rock)
magma erupts and solidifies
- molecule is the mian component in most magma
- silicon ion (Si4+) bonded to 4 oxygen ions (O2-) in the shape of a tetrahedron. =SiO2
- magma cools, forming chains and networks
- The arrangement depends on temperature, pressure, and other available elements
- (such as Mg, Fe, Al, Ti, Na, K, etc.)
Si and O ions make up about 50%–90% of most magmas and Al, Ca, Fe, K, Mg, Na, and Ti
Ba, Cr, Mn, Ni, P, Sc, Sr, Zn, and many others.
Each type of mineral
- different crystalline structure & chemical composition
- characteristic range of T, P, and magma composition at in which it will grow.
- Some crystallize at higher temperatures
- If cools too quickly, no minerals will have time to grow.
Magmas can have complex cooling histories
- larger crystals crystallized early while the magma was still underground =cooled slowly
- smaller crystals formed only after the lava erupted = cooled quickly.
- Porphyritic texture
- The ordered structures of molecules
- As a magma continues to cool, the polymers settle into ordered structures as they search for their minimum energy state.
- As a magma cools, the minerals that crystallize first are those with the highest melting temperatures.
- As the magma continues to cool, addition minerals with lower crystallization temperatures begin to crystallize.
Olivine & Pyroxene
higher in heavy elements (Mg, Fe, and Ca) lower amounts of light elements (such as Na and K).
- Separation of the crystals from the magma
- a fraction of the original magma is removed when the crystals are separated from it
- Fractional crystallization takes magmas that were high in Mg-Fe (mafic), and turn them into magmas low in Mg-Fe, but high in K, Si, etc. (silicic)
Igneous Rocks classified according to two parameters
- 1. Texture (grain size, vesicularity)
- 2. Chemical Composition (indicators are minerals and color)
Classified by composition
- which is mostly determined by how much partial melting created them
- how much fractional crystallization has occurred
- Si content is often used to summarize the classification because Si increases with increasing fractional crystallization.
- Lowest Si, highest Fe and Mg
- very dense.
- Ultramafic magmas that do not reach the surface crystallize to peridotite,
- If they reach the surface they form a rare volcanic rock called komatiite.
- Low Si, high Fe, Ca and Mg
- In all tectonic settings, but most abundant in hotspot & continental rift/mid-ocean ridge settings.
- Mafic magma crystallizes into an intrusive rock called gabbro or volcanic rocks called basalt and basaltic andesite
- Moderate Si, high Ca and Al
- Erupt in subduction zones.
- Intermediate lava crystallizes into diorite, or a volcanic rock called andesite (named after the Andes mountains) and dacite.
- High Si, Al, K, Na (low Fe, Mg).
- Erupts on thick crust in subduction zones.
- Silicic lava crystallizes into rhyodacite and rhyolite, or granite if it is intrusive.
Key Properties of Magma
- Viscosity: A measure of how much something resists flowing
- Silica content: More viscous with increasing silica content
- Temperature: Magmas, like many fluids, get more viscous as temperature decreases.
- Density: Mafic magmas are denser because they contain more of the heavier elements
- Volatile content: All magmas have some volatile gasses dissolved in them, water, CO2 , S, F and Cl.
Properties of Magma
- Magmas that are hotter, less viscous (runnier), and less volatile-rich (less gassy) tend to erupt effusively (calmly).
- Magmas that are stiffer (more viscous) and more volatile-rich (gassier) tend to erupt explosively
- Basalt and Basaltic Andesite = Usually Effusive
- Rhyolite and Rhyodacite = Usually Explosive
- Andesite and Dacite = Either
Innards of a Volcano
- Volcanic Vent or Crater
- Volcanic Conduit (Neck)
- Magma Chamber
- Volcanic Apron
Volcanic Vent or Crater
Where lava leaves the volcano is called the vent, or crater if it is a depression. May be located at the top, side, or edge of the volcano
Volcanic Conduit (Neck)
This is the path that magma takes to get to the surface. After the volcano has gone extinct and the outer parts are eroded, the solidified conduit that is exposed is called a “volcanic neck” (Mt. Washington, Mt. Thielsen).
This is where most fractional crystallization occurs, so magma here contains many crystals and is sometimes called a “crystal mush”.
Volcanic rock and/or tephra (loose volcanic debris) that surrounds the vent. It can be very steep or gently sloped, depending on the material.
- Volcanic Types
- Created by a single eruption (may be over a number of years, but once it goes dormant it does not reactivate). Typical of small volcanoes such as scoria cones (aka cinder cones).
- Volcanic Types
- Created by multiple eruptions, even over thousands or millions of years. Most volcanoes, and probably all large ones, are polygenetic.
- Essential material and driver
- Any erupted material, such as lava, tephra, and volcanic gases, that actually came from that volcano’s magma chamber during the eruption. This is what creates and drives the eruption, and usually makes up the largest portion of erupted material.
- Not Directly related to the eruption
- The magma chamber may become incorporated into the magma on it way out of the volcano. These bits of other rocky debris are called accidental, and can come from a previous eruption or from other rocks under the volcano.
- Due to rapid escape of volatiles from the magma.
- Silicic lavas (dacite, rhyolite) have the high viscosity and volatile contents that typically lead to explosive eruptions.
- Create abundant tephra.
- Can also occur when magma encounters external water such as an ocean, lake, glacier, rain, or groundwater. (hydromagmatic eruption).
- Fairly calm eruptions that produce lava flows and lava domes.
- Typical eruptive style for mafic lavas with low viscosity and low volatile contents (basalt, basaltic andesite),
- Can also occur in silicic lavas that have degassed their volatiles.
The eruption may be centralized at or near the top of the volcano.
Some eruptions are on the flank of the volcano.
An eruption can occur simultaneously on the summit and the flank.
An eruption can occur on the periphery of a volcano, not directly related to activity at the main vent.
- Lava that erupts from cracks a few hundred feet to a few miles long.
- Early stage may include tall spurts of lava (“fire fountaining”) that produce some minor basaltic tephra.
- Mostly produces thin, runny basalt lavas that can travel 10–100 km or more.
- The largest lava eruption in historic times (1783, Laki, Iceland) was a fissure eruption.
- Massive floods of basaltic lava covering large areas (flood basalts) are caused by unusually intense fissure eruptions. (Columbia River Basalts)
- Enormous edifice, low profile, gentle slopes.
- The largest volcano on Earth (Mauna Loa) is a shield volcano.
- Made of low viscosity and low volatile content basalt lava flows that are able to spread over a large area.
- Summit eruptions and rift eruptions along the flanks of the volcano are common.
Scoria Cone (Cinder Cone)
- Small, steep-sided cone made of basaltic tephra (called cinders or scoria) ejected from a vent. Many have a lava flow extending from their base.
- The loose material piles up near the vent at the angle of repose
- Usually monogenetic.
- Composed of basalt or basaltic andesite, with low viscosity but high enough volatile content to eject tephra.
Composite volcano (stratovolcano) Simple cone
- Often a beautifully conical, radially symmetric mountain. Like a grand cinder cone.
- Typically formed by repeated eruptions over a long time (polygenetic), but all from the summit vent.
- Composed of relatively low viscosity basalt and basaltic andesite flows and tephra.
- Long-lived volcanic center with a complex eruptive history: multiple lava and tephratypes from multiple vents over 10,000 to 1,000,000 years or more.
- Andesite, dacite and rhyodacite lavas (high viscosity and high volatile content), tephra, and pumice. Explosive eruptions common.
- Most subduction-related (volcanic arc) volcanoes
Tuff Ring & Tuff cone
- Circular feature constructed of basaltic tephra.
- Interaction of basaltic lava with external water near the surface,
- Like scoria cones that erupt in water
- Steam explosions propel tephra high into the air, & steep pile of wet tephra forms where it lands
- Sides are steeper than a cinder cone because wet tephra is stickier than dry tephra
- Tuff rings are hollow and broad, tuff cones are more cone-shaped.
- Underground explosion due to rising magma interacting with external water (usually groundwater).
- There may be very little juvenile material involved in the explosion.
- Explosion excavates a pit (usually <1 km across and 100 m deep) that looks like a meteorite impact crater.
- Small, steep-sided, dome-shaped feature.
- High viscosity lava (dacite, rhyodacite or rhyolite) low in volatile content.
- Usually caused by a single eruption from a single vent beneath the dome.
- Erupts effusively and very slowly, but the dome can collapse and form a dangerous, fast-moving flow of hot rocks and ash.
- Steep-sided feature formed during a sub-glacial eruption.
- Lava erupts under a glacier cools very quickly and cannot travel far
- It is constrained by the glacier into a steep-sided hill.
- Can either melt all the ice or emerge through the top of the ice to create normal-looking basalt.
- Inward collapse of the summit area of a volcano, after the rapid emptying of a magma chamber by a large eruption. Collapse feature at least 1 km in diameter
- Calderas and craters are sometimes confused because both appear after violent eruptions, but careful study of the deposits on the floor of a caldera reveals that the top of the volcano collapsed down into the caldera.
- involves external water such as an ocean, lake, glacier, rain, or groundwater.
- This can affect the style of the eruption because water explodes into steam when it encounters magma, which can turn an otherwise effusive eruption into an explosive one
Two types of hydromatic eruptions
- Phreatic – explosions of steam only, with no juvenile material.
- Phreatomagmatic – explosions of steam that include juvenile material
is a measure of the size and explosiveness of an eruption
Eruptive Power define by:
- Dispersal: total area covered by tephra (in km2).
- Fragmentation: size of tephra pieces.
- Intensity: rate at which material erupted (in kg/sec).
- Magnitude: total volume of erupted material (in km3)
Volcanic Explosivity Index (VEI)
- Chris Newhall & Steve Self (1982)
- based on total volume of erupted tephra
- Relationship between the size of eruptions & the length of time between eruptions of that size – larger eruptions occur much less frequently than smaller ones.
- Basalt and Basaltic Andesite: Usually aphanitic or porphyritic, sometimes vesicular.
- Typical eruption temperature is approximately 1100°C.
- 1. Found in all tectonic settings
- 2. Especially common at mid-ocean ridges & intraplate (hotspot) islands
- 3. Low viscosity and usually low volatile content
- 4. Usually erupt effusively.
- 5. Some mafic volcanoes are volatile-rich
- 6. External water can also cause explosive eruptions
- Phase 1: Inflation
- Phase 2: Dense Fumes
- Phase 3: Fragmental Ejecta
- Phase 4: Curtain of Fire
- Phase 5: Central Vent
- Relatively small eruption (low on VEI) that produces a small, cauliflower-shaped eruption column.
- Common as flank eruptions on larger volcanoes.
- Typically create cinder cones.
- Usually basalt or basaltic andesite
- eruption columns
- Usually basalt, but may be andesite or dacite.
- Erupt tephra, lava flows uncommon.
- Typically occur at composite volcanoes
- Usually basalt
- Lots of interaction with external water
- Jets of black tephra with white steam
- 95% tephra and ash
- Forms a tuff ring or tuff cone
- A flow with a rough rubbly surface composed of broken lava blocks (called clinkers) surrounding a thick, hot core.
- Flows like a tank tread rolling over earlier clinkers.
- This causes rubble zones above and below the lava flow
Lava with a smooth or ropy surface. Advances as a series of small lobes and toes that continually break out from the leading edge of the cooling crust
- Active lakes have a partially cooled crust 5–30 cm thick,
- Only a few minutes or hours old.
- Crust continually forms, circulates, breaks, and sinks into the moving lava below (like a miniaturized version of plate tectonics).
- Lavas reach water, cool quickly & pile up into steep benches.
- Not stable & very dangerous to walk on.
- Hawaiian lava benches have collapsed into the ocean without warning, killing the tourists standing on them.
- Lava encounters water, violent steam explosions
- Forms basaltic tephra that piles up on the shoreline.
- Similar to a cinder cone except that it is rootless (its lava source is a vent somewhere upslope, not beneath it).
Rapidly cooling blobs of lava that quickly form a chilled glassy margin. Lava breaks through the crust and squirts out to form another pillow.
large volumes of basalt lava that erupted in a short period of time
- shooting a column of ash high into the atmosphere.
- Pliny the Younger
- Produce: ash fallout, pyroclastic surges and flows, block & ash flows (nuee ardentes)
Ashfall or Fallout
- Tephra rains down from eruption column
- Widely distributed
- Draped over topography
- Made up of angular fragments
- Large frags first
- Rapidly decrease in thickness
ground-hugging avalanche of hot ash, pumice, rock frags, and gasses
Causes of pyroclasitc flows
Dome collapse, dome explosion, collumn collapse
- low density, very turbulent mixtures of mostly gasses, plus some ash and small rock fragments.
- They surge outward from the base of an eruption column or the advancing front of a pyroclastic flow.
- Because surges are low density, they tend to spread over large areas and move up and over ridge crests easily.
Block and ash flow
- Composed of hot ash and blocks.
- Caused by collapse of a lava dome that became too tall or steep to support itself.
- Can also be caused by collapse of an eruption column.
- Do not contain pumice, only blocks, crystals, and ash
- Tend to be made of lava flows interlayered with tephra.
- Usually either simple cones or composite volcanoes.
- Lavas are more viscous than mafic lavas, so can form steeper slopes.
- May also erupt some mafic and silicic compositions.
- Central Zone (0–5 km): Lava flows and pyroclastic flows are hazards here, but steep slopes prevent much from depositing here.
- Proximal Zone (5–15 km): Lava flows and pyroclastic flows are at maximum thickness.
- Distal Zone (>15 km): Mostly lahars, a few pyroclastic flows may make it this far.
- Silicic volcanism is most commonly found at continental arcs (e.g., Cascades), continental hotspots (e.g., Yellowstone), or continental rifts (e.g., Rio Grande Rift).
- Large silicic eruptions can produce over 1000 km3 of tephra, ash-flow tuffs, and ashfall deposits, create a caldera at the source vent. Ashfall can spread thousands of km downwind of the vent.
Silicic Lava Properties
- Very viscous
- High Volatile Content
- Explosive Eruptions
- Gas bubbles have a hard time escapting silicic
- Bubbles stretch = Frag. rock into pumice and volcanic ash
- Gray to pinkish white
- volcanic glass, usually rhyolitic in composition (occasionally dacitic) and black in color (sometimes brown).
- The lava cools too fast for crystals to have time to grow.
- Glass, unlike crystals, has no regular structure and therefore fractures in smooth curved (conchoidal) shapes.
- The intersections of these fractures can form sharp edges, so obsidian is used to make arrowheads and cutting tools.
- porous volcanic rock that forms during explosive eruptions.
- It consists of a network of gas bubbles amidst fragile volcanic glass and minerals.
- Pumice is a volcanic version of the foam generated when a bottle of pressurized soda is opened, but this “foam” can solidify, usually in stretched and twisted shapes.
Styles of Silicic Volcanism
- Effusive eruptions create rhyolite domes and flows (obsidian if glassy)
- Explosive eruptions create tuffs (called ash-flow tuffs or ignimbrites if large).
- Silicic lavas are erupted from: Individual vents (domes), Composite volcanoes, Calderas
- flattened pumice
- pumice is heated and squeezed inside an welding ash flow tuff to form streaks of dark glass.
Ash Flow Tuffs (Ignimbrites)
- 100-1000 meters thick
- Thin surge deposit at its base
- Thick tuff and hot = welding of ash and pumice
- 1. Uplift
- 2. Ring fracture eruption
- 3. Collapse
- 4. Post-collapse volcanism
How water moves around in a volcano
- 1. Rain water seeps into ground
- 2. Groundwater is heated by hot volcanic rocks
- 3. Underground boiling separates hot gas and liquid brine (loaded with dissolved salts)
- 4. Hot springs, vapor, salty brine
- Volcanic glass is exposed to water it becomes cloudy
- Higher temp. accelerates process
- Hot gasses (water vapor) promte devitrification.
Vapor Phase Alteration
- Exterior of Ignimbrite
- Devitrification conduits where the hot gasses escape.
- Simple Caldera
- Overlapping Caldera
- Nested Caldera
Medicine Lake, California:
Basin & Range meets Cascades
- ~50 km to the east of the main volcanic arc, believed to be a result of the interaction between Cascades volcanism and Basin-and-Range volcanism.
- Caldera surrounded by lava fields & domes of over 600 km3 of material.
- Most recent eruption (Glass Mountain Rhyolite) occurred ~1000 y ago.
- Active fumaroles attest to its potential for continued activity.
Mt. Shasta, California:
Collapse and Rebuild
- The largest Cascade volcano, and one of the largest composite volcanoes in the world, containing more 350 km3 of erupted material.
- Active for at least 600 k.y., repeated gigantic collapses on a much larger scale than the 1980 Mt. St. Helens collapse and landslide.
- Debris flows due to heavy rains or snowmelt are a frequent problem.
- Appears to erupt every 600 years or so, last eruption a small one in 1786
Lassen Peak, California:
Shasta's Noisy Neighbor
- Southern Cascade volcano had the second-most recent eruption- 1914.
- Mostly domes and lava flows, active since at least 600 k.y. ago.
- Many fumaroles and mudpots.
- The 1914–1917 eruption comprised lava flows and domes that produced a number of ashfall deposits, and a large mudflow that traveled 50 km
Volcanic Hazards Fatalities
- Famine/Disease: 30%
- Pyroclastic Flows: 27%
- Lahars: 17%
- Tsunamis: 17%
- Debris: 4%
- Airfall: 4%
- Volcanic Gasses: <1%
- Lava Flows: <1%
- Jokulhlaups: <0.1%
- Biggest killer from volcanoes is the indirect consequences: Famine and disease.
- Eruption destroy farmable land, contaminate water supplies, and make buildings unusable.
- Dome collapse, explosion, or column collapse
- Hot, fast and deadly
- Surviving one is unlikely
- Volcanic Mudflows - needs only 10% water
- Hot volcanic material melts snow or ice, rainfalls on loose
- Can occur during or after an eruption
- Follow river valleys for many miles
- Large chunk of a volcano collapses
- May or may not be eruption-related
- Debris flow, landslide, or large pyroclasitc flow enter a body of water
- Travel hundreds to thousands of kilometers in deep ocean
Volcanic Tsunami: Krakatau, 1883
- Island was uninhabited
- 36,000 people died from the resulting tsunami
- Caldera collapse underwater eruption, or volcanic landslide can trigger tsunami
Airfall - Bombs and Ash
- Falling ash and bombs damage crops, structures, & water supplies
- Falling volcanic bombs are very dangerous, but do not travel far.
- Volcanic ash can collapse rooftops. Wet ash is especially heavy.
- Ash makes it difficult to breathe, blocks sunlight, stalls airplanes.
- Rain can turn fallen ash into lahars
Health Effects From Volcanic Ash
- Inhaled deeply in the lungs.
- Short-term exposure: cause eye, nose & throat irritation.
- Long-term: Breathing
- Runny Nose
- Sore Throat
- Worsening of pre-existing respiratory conditions
- Difficulty Breathing
- Eye and skin irritation
Eruption of Mount Redoubt, 1989
- All four engines shut down
- Aircraft descended from 27,900 ft - 13,300 ft
- - Mountains in this region reach 11,000 ft
- $80 million in damages
- Deadly in high concentrations (SO2, CO2, and F)
- Lower concentrations causes repiratory problems and pollutions.
- Concentrates in plants and livestock after digestion
- Iceland (1783) Laki volcano
- Elk and deer Yellowstone NP (chronic teeth & bone)
- Hazardous to property
- Land becomes unusable
- Niyaragongo volcano, Zaire (1977) ; killed 300 people
- Icelandic word: glacial outburst flood triggered by volcanic activity
- Volcano erupts underneath glacier, melting ice accumulates huge amounts of water under glacier
- Carrying large chunks of ice and some volcanic debris
- ~15,000 yrs. ago; ice dam blocked off the Clark Fork River
- Lake drained in ~ 48 hours
- Periodcially dam would fail
- Numerous massive floods from glacial lake in Montana
- Roared across E. Washington & down Columbia
Conceptual Block Model
- Arc: lots of slab influence + a little continental influence
- HLP: a little slap influence + lots of continental influence
HLP vs. Cascades
- HLP volcanism has a different morphology than Cascades
- HLP is time-transgressive, Cascades and Newberry are not
- HLP is bimodal, Cascades are notVolcanic morphology is related to both “age behavior” and chemistry
- Cinder Cone Eruption (1973)
- Lava flows encroached town and almost blocked harbor
- Sprayed 1.6 billion gallons of seawater; 1/3 town destroyed
- Eruption added corner, narrow harbor better for protection of storms.
Mt. Etna, Italy
- 1669 flow diversion attempt by humans
- Levee breached with picks & shovels, diverted away from Catania
Mt. Rainier, Washington
- Lahar detection and warning system installed
- Auto. radios Emergency Response office in Seattle
- Warning sirens triggered, post evacuation routes lead to high ground
Lake Nyos, Cameron
- CO2 asphyxiated 1700 people in villages near Lake Nyos in 1986.
- Volcanic gasses accumulated in water at the bottom of lake until suddenly released.
- Now a tube system in the lake that constantly pumps water from the bottom up to the surface to allow the gasses to escape gradually, not accumulate
Volcano Disaster Assistance Program
- Quick Response to any location
- Saved lives at Mt. Pinatubo in 1991
- Andesite & dactie stratovolcano
- 12,276 ft
- Located w/ in coeval volcanic field of primarily basalt
- Last eruption 1000-3500y.b.p
- Native Americans call it Pahtoe
- Lahars (traveled 52 miles)
- Debris avalanches (traveled 40 miles, 1921)
- Regions of potential activity.
- Seismic activity using existing regional networks.
- Remote sensing (satellites) to look for temperature changes and ground uplift
- An individual volcano that showed signs of activity: Intensive seismic monitoring using a local network
- Hydrologic monitoring (river & hot-spring flows & temperatures)
- Monitoring volcanic gas emissions
- Monitoring ground deformation (detect swelling or subsidence), and changes in gravity and magnetic fields due to magma movement
- Pacific Northwest Seismograph Network (PNSN) The types and depths of earthquake (a.k.a. seismic) activity are important in predicting eruptions.
- Seismometers also detect tiny ground motions caused by other types of phenomena
Anatomy of Earthquake Waves
- Amplitude (height of waves in the train = amount the ground moved)
- Frequency (number of waves that arrive each second = shakes per second)
- Duration (length of wave train from beginning to end = how long shaking lasts)
Types of Earthquakes
- 1. Tectonic earthquakes
- 2. Shallow Earthquakes
- 3. Surface Events
- 4. Harmonic Tremor
- Located away from the volcano.
- Produce a sharp first-arrival, high-frequencysignatures, and have deep (>3 km) sources.
- Caused by tectonic plate motion, = background noise.
- Under the active volcano at depths <3 km.
- Similar wave trains to tectonic earthquakes, but are smaller and shallower.
- Caused by rocks fracturing as magma and volcanic gas move deep beneath the edifice.
- Waves arrived abruptly & shaking is over in 10 sec.
Shallow earthquake wave train in the upper panel, and the waves train's in the lower panel.
- Gas and tephra explosions, rockfalls, and snow and rock avalanches from the crater walls, produce complicated signatureswith gradual beginning and end.
- Seismic waves from a surface event build up gradually (at ~22 sec in figure), and continue unevenly for more than 30 sec
- Long-lasting, very rhythmic signal probably related to movement of magma and volcanic gasses toward the surface.
- It has a larger amplitude and more low-frequency energy than tectonic earthquakes.
- This is the earthquake type most often (not always) indicative of an impending eruption.
- Harmonic tremor waves arrive gradually (starting at ~2 sec mark on this record) and continue for a long time
Surveying River Channels
- Hydrologic Monitoring
- Lahars need to go somewhere. Monitoring changes in the shape & size of a river channel helps track erosion and deposition.
- Hydrologic Monitoring
- Instruments measure volumes of water & sediment using:
- Manual measurements from bridges and cables
- Automatic recording of a river's water depth at gauging stations
- Hydrologic Monitoring
- Samples from the bottom of the channel to see what is moving.
Potential Sources of water in hot springs around volcanoes
- Meteoric water (water from precipitation)
- Surface water
- Magmatic fluids (this is the one most relevant for volcano monitoring)
Certain chemical substances in hot springs indicate potential volcanic activity
- Cl concentration (Cl output is directly proportional to the heat discharged)
- SO2, a magmatic gas
detects changes in the release of certain gasses from a volcano (chiefly CO2 and SO2)
- Track ash clouds: AVHRR (Advanced Very High Resolution Radiometer) & MODIS(Moderate-resolution Imaging Spectroradiometer)
- Measure ground deformation: InSAR (Interferometric Synthetic Aperture Radar)
- Measure gas (especially SO2) and/or heat: TOMS (Total Ozone Mapping Spectrometer)
reducing the risk from volcanic activity
- Long-term solutions to understand likely effects of an eruption & prepare residents for those effects
- Short-term solutions to detect an eruption & remove people from the vicinity or divert the eruption away from population.
Four Key Components make for successful mitigation
- 1. Good science and research
- 2. Outreach and education
- 3. Practice and drills
- 4. Monitoring and early warning
Volcanoes create new land
- Lavas erupt and tephar is deposited, new lands can be created.
- Surtsey, Iceland
- Home Reef, Tonga
Volcanoes create fertile soil
- Volcanic materials are rich in mineral nutrients, so volcanic soils are very fertile.
- Good rice growing regions in Indonesia
- The civilizations of Rome and Greece excellent vineyards & olive groves.
- Coffee, pineapple, sugar cane, & macadamia nut plantations in Hawai’i
Water is heated by hot volcanic rocks or magma, creating two important benefits of volcanic activity: energy and mineral deposits
- High temperature - Electricity is produced in geothermal fields by circulating water through hot rocks until it turns into steam, which is pumped back to the surface to drive turbines connected to generators.
- Low temperature - Hot water can be pumped directly into the heating systems of buildings. 70% of the homes in Iceland are heated this way.
- Byproducts - Some geothermal systems also produce byproducts such as gold, mercury, silver, and sulfur.
The Geysers, California
- Near Santa Rosa, is the largest geothermal field in the world
- Produces 2000 megawatts (MW) of electricity
- Enough to power 2 cities the size of San Francisco
Volcanic Mineral Deposits
- Valuable mineral deposits form from geothermal activity in volcanic rocks. Includes Cu, Sn, Au, Ag, Zn, Ni, Cr, S, and many others.
- Form beneath the surface. Hot water leaches tiny amounts of metals from large bodies of hot rock. Waters cool upon migration into cooler surrounding rocks. Metals come precipitate into enriched veins & metallic bodies.
- Most diamonds are mined from a rare volcanic rock calledkimberlite
Chilean Copper Belt
- Berkeley Pit Mine (Butte, Montana) - Superfund Site
- Bingham Canyon Copper Mine (Utah)
- Mid-Ocean Ridges
- Hot fluids percolate through the volcanic system at a ridge and bring up hot, mineral-rich fluids.
- Minerals rich in S, Fe, Cu, Zn, Pb, & Ni precipitate into towers referred to as “black smoker chimneys”
Industrial Products of Volcanoes
- One of the most important is sulfur used to produce sulfuric acid and fertilizer.
- A sulfur mine near the summit of Volcan Aucanquilcha in Chile (~5800 m or ~19,000 ft).
- This mine removed sulfur as it was being deposited on the summit and slopes by active geothermal activity
Used as abrasive and cleaning product, including making stone-washed jeans. Pumice is mined in Italy, South America, and California, Oregon.
- Bentonite is a clay formed from altered volcanic ash.
- It has an exceptional ability to absorb water, ammonia, and odors.
- Used in drilling mud for oil and water wells, polishing, papermaking, and as a clumping agent in cat litter.
- It is also used as an emulsifying agent in soft-serve ice cream
Used as a road-building material, and is spread on icy roads in winter to improve traction
- Most volcanic rocks, when unaltered, make excellent building stones.
- Basalt, granite, and welded tuff are especially strong and hard, and are often decorative as well
- Tourist economies build up around volcanoes that are popular destinations for recreation such as skiing, hiking, and climbing.
- Volcanoes with religious significance are visited on pilgrimages.