lec5-volcanism

8/7/2019 lec5-volcanism

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VOLCANISM

VOLCANISM

FACTORSAFFECTINGTHENATUREOFVOLCANICERUPTIONS(VISCOSITY):

a. composition of magma: SiO2 content = viscosity

Basaltic lavas: viscosity = quieteruptions (ex. Hawaii)Andesitic/Rhyolitic lavas = viscosity = explosive eruptions (ex. Mt. St. Helens)

b. temperature: temperature = viscosityc. amount of dissolved gases (H2O, CO2, etc.): amount of dissolved gas =

viscosity

CAUSESOFERUPTION:1. due to decompression2. due to interaction of water with ascending magma

MATERIALSPRODUCEDDURINGANERUPTION:

a. Lava Flow - a 'stream' of molten rock.'aa' lava flow- jagged, rubbly, broken surface'pahoehoe' lava flow- smooth, ropy surface

b. Pyroclastic debris - hot, broken fragments of rock ejected and blown from the

volcano's vent during explosive eruptions

Tephra - deposits (piles) of pyroclastsvolcanic bombs and blocks (>64mm)

bomb ejected as incandescent lava; streamlined shapeblock made of hardened lava; angular shape

lapilli (walnut-sized: < 64mm)cinders (pea-sized) contain numerous voids and formed when ejected

lava blobs are pulverized by the escaping gases

ash and dust (very fine, < 2mm)

Pyroclastic flows composed of highly mobile tephra flows rushing down theflanks of a volcano

c. Gases compose 1-5% of the magmas total weight

H2O (70%)CO2 (15%)N2 and nitrogen compounds (5%)

sulfur compounds (H2S, SO4, SO2, etc.) (5%)minor amounts of Cl, H2, Ar, etc.NO free oxygen

cbd ntr / geology 11 lecture / july 2002


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VOLCANISM

d. Nue ardente (glowing avalanches)- glowing clouds of volcanic gases (steam)and pyroclastic debris (ash) which avalanche down the side of avolcano, and can reach speeds of 125 mi/hr (200 km/hr)

Mount Pelee, Caribbean island of Martinique (1902) - destroyed the town ofSt. Pierre, killing almost all of its 28,000 inhabitants at once (a prisoner in adungeon, a shoemaker, and a few people on ships in the harbor survived)

VOLCANIC ERUPTIONS

A. Non-explosive (e.g. Hawaii)

1. Magmas. low-viscosity and have high dissolved gas content and less silicacontent than explosive eruptions.

2. Volcanoes. Broad, dome shaped structures having slopes of only a few degreesup to 10 degrees. The very broad dome-shaped structure is called a shield volcano.

B. Explosive (e.g. Mt. St. Helens)

1. Magmas. Characterized by high-viscosity magmas and low dissolved gascontent, high silica content.

2. Volcanoes. Steep-sloped, conical shaped volcanoes called strato-volcanoes.These are built up of tephra deposits and viscous lava.

UNDERWATER ERUPTIONS: MID-OCEANRIDGESpillow basalts - pillow-shaped blobs of basalt resulting from volcanism on the

ocean floor

MAJORERUPTIONSINTHE WORLD

1. 1883 Krakatoa, Indonesia: explosion heard around the world (4800 km away);18 km3 of volcanic debris ejected

2. 1815 Mt. Tambora, Indonesia: ejection of 30 km3 of volcanic debris; caused"year without a summer" (global temperature drop); ash in atmosphere blocksincoming sunlight and reflects it back into space (vivid sunsets)3. May 18, 1980 Mt. St. Helens, Washington State: for comparison, only 1 - 2 km3

of volcanic debris was ejected.



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VOLCANISM

4. 5000 BC, Mt. Mazama, Oregon: explosion ejected 40 km3 of volcanic debris;magma chamber collapsed to form a caldera; when filled with water, it is called acrater lake

5. 1902 Mt. Pelee, Martinique (Carribbean)6. April 4, 1982 El Chichon, Mexico: associated with El Nino climatic abberation

7. June 15, 1991 Mt. Pinatubo, Philippines: ejection of 2 miles3 of dust and fineash; destroyed more than 42,000 homes and 100,000 acres of cropland; killedapproximately 900 people; evacuation and abandonment of Clark Air Force Base(US); eruption was predicted 1 month in advance and monitored; SO2 aerosol cloudcircled Earth in just 21 days; stratospheric haze caused a 1 degree temperaturedrop (global)

VOLCANOES

A volcano is a mountainous accumulation of material resulting from successiveeruptions of lava from a central vent.

BASICPARTSOFAVOLCANO

Crater a funnel-shaped depression at the summit of a volcano, from whichtephra, gasses and lava are emitted

- connected by a vent or pipe to the magma chamber below

Caldera - crater more than 1 km in diameter, formed at the summit of avolcano when lava is drained from an underground magma chamber, causingthe summit of the volcano to be unsupported, and to collapse; frequentlywater-filled

Pit crater - collapse features on the flanks or summit of a volcano that aresmaller than the main caldera at the summit of a volcano

Vent - pipe-like conduit from the magma chamber to the surface

Fumaroles - secondary vents on the flank of a volcano which emit steam andother gases

Kilauea - the world's most active volcano, and has been erupting continuouslysince January 3, 1983- rarely erupts from its summit, instead it erupts from vents on its flanks- summit of Kilauea is about 4000 feet above sea level



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VOLCANISM

TYPESOFVOLCANOES

Viscosity of the magma controls the type (shape) of volcano and its explosivity.

1. Shield- resembles a Roman shieldlying on the ground

- basalticcompositionlow viscositylava relatively quieteruptions- slopes are gentle: 15 degrees or less, and steepening on the edges wherelava is cooler and more viscous

- successive lava flows and limited tephra- probably the largest volcanoes on earth

Mauna Loa (on the Big Island of Hawaii)

- the largest active volcano in the world- last erupted in 1984 (14 times in the 20th Century, and 37 times since1832)

- the most massive mountain on Earth, rising to an elevation of 13,677feet above sea level, or 31,677 feet above the sea floor (volume is

10,000 miles3)

Mauna Kea (on the Big Island of Hawaii)- rises to an elevation of 13,796 feet above sea level, or 31,796 feet

above the sea floor

Olympus Mons (or Mount Olympus)- the largest volcano in the Solar System located on the planet Mars- it is three times as high as the largest volcanoes on Earth (nearly 27km high

2. Cinder Cone- relatively small (less than 300 m or 1000 ft high)

- relatively steep slopes (30 - 40 degrees) due to high angle of repose of ash- made of pyroclastic material

The volcano Paricutin, in Mexico, is a well-known example of a cinder cone.

3. Composite Volcano orStrato-volcano- make up the largest percentage of the Earth's volcanoes (about 60%)- high silica content(sialic or intermediate) with composition of andesite,

dacite, and occasionally rhyoliteviscosity usually explosive

- layered structure; also referred to as composite (combination of tephra andlava flows)

http://volcano.und.nodak.edu/vwdocs/planet_volcano/mars/Shields/Overview.htmlhttp://volcano.und.nodak.edu/vwdocs/planet_volcano/mars/Shields/Overview.html


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VOLCANISM

- can grow very tall and large (1 - 10 km across)- commonly found along subduction-related volcanic arcs- nue ardente and lahar(mudflow) are usually observed

Mt. Vesuvius, Cascade Range volcanoes such as Mt. Rainierand Mt. St. Helens

Mt. Mayon, Philippines and Mt. Fujiyama, Japan

*OTHERTYPESOFVOLCANOES (MGABULKANGHINDIMUKHANGBULKAN!!)

1. Large rhyolite caldera complexes- most explosive of the Earth's volcanoes- usually so explosive when they erupt that they end up collapsing in onthemselves rather than building any tall structure calderas (e.g.

Yellowstone, US)

2. Monogenetic fields- a collection of numerous separate vents and flows- product of very low supply rates of magma- it is like taking a single volcano and spreading all its separate eruptionsover a large area (e.g. Michoacan-Guanajuato field, Mexico)

3. Flood basalt provinces

- fluid, waterlike, basaltic lava flows that cover an extensive area- parts of the world covered by thousands of square kilometers thickof basalt lava flows (e.g. Columbia River Basalts, US; Deccan Traps,NW India)

4. Mid-ocean ridges- occurs at plate margins where oceanic plates are created (e.g. GordaRise MOR separating Juan de Fuca plate from the northern part of thePacific plate)

- some consider MORs as the largest volcanoes on Earth

DISTRIBUTIONOFVOLCANOES

1. Pacific Ring of Fire. surrounds the Pacific Ocean; subduction zonevolcanism

2. Hot spots. Hawaiian Islands, mantle plumes; intraplate volcanism3. Spreading centers. mid-ocean ridges (Iceland), rift valleys (Mt. Kilimanjaro,

Africa); spreading center volcanism

*optional



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VOLCANISM

*Types of volcanic eruptions:

1. Icelandic basaltic lavas from fissures: Laki Fissure, Iceland2. Hawaiian entirely volcanic; outpourings of fluid basaltic magma: Hawaii3. Strombolian incandescent lava + clouds: Stromboli, Sicily

- moderate explosivity but eruptions may continue for long periodsof time

- flows alternate with pyroclastic debris: composite cone

4. Vulcanian more explosive than Strombolian eruptions: Cerro Negro, Nicaragua- abundant pyroclastic debris

5. Pelean highest viscosity and most eruptive/explosive: Mt. Pelee- distinguishing feature: nuee ardente (ash and associated lava flows)

*rarely used in describing explosivity of eruptions

VOLCANIC ACTIVITY IN THE PHILIPPINES

active tectonic setting: subduction zones scale and type of volcanism varies from monogenetic cinder cones to largestratovolcanoes and calderas

composition of volcanic rocks range from tholeiitic basalt to andesite toshoshonite

volcanoes of the Philippines are the most deadly and costly in the world mudflows and tsunamis are more common in the Philippines, compared to otherregions, because of heavy rains

VOLCANIC HAZARDS

can be quantified by specifying the probability of a specific event (e.g. apyroclastic flow of a given volume from a volcano, happening in a specific timeinterval in a specific spatial area)

construction of this probability would consist of the history of known eruptionsas well as the tectonic setting

early warnings and premonitory phenomena:a. changes in melt and gas chemistryb. regular small ground motions having a near constant frequency measured

by seismographs (harmonic tremors)

http://volcano.und.nodak.edu/vwdocs/vwlessons/volcano_types/index.htmlhttp://volcano.und.nodak.edu/vwdocs/glossary.html#Shoshonitehttp://volcano.und.nodak.edu/vwdocs/vwlessons/volcano_types/index.htmlhttp://volcano.und.nodak.edu/vwdocs/glossary.html#Shoshonite


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VOLCANISM

c. deformation of the surface of the volcano measured surveying techniques,including space geodesy

TYPESAND EFFECTSOF VOLCANO HAZARDS(www.usgs.gov)

1. Volcanic Gases- spread primarily as acid aerosols (tiny acid droplets), compounds attached to

tephra particles, and microscopic salt particles

- undergo a tremendous increase in volume when magma rises to the Earth'ssurface and erupts (the main driving force of explosive eruptions)

Effects:a. Sulfur dioxide (SO2)

- WHO recommends a concentration of no greater than 0.5 ppm over 24 hoursfor maximum exposure (6-12 ppm: irritation of the nose and throat; 20 ppm: eye

irritation; 10,000 ppm: irritate moist skin within minutes)- volcanic smog, global cooling and ozone depletion

b. Hydrogen sulfide (H2S)- colorless, flammable gas with a strong offensive odor (sewer gas)- low conc.: can irritate the eyes and acts as a depressanthigh conc.: can cause irritation of the upper respiratory tract and, during long

exposure, pulmonary edema

- 30-minute exposure to 500 ppm: headache, dizziness, excitement,

staggering gait, and diarrhea, followed sometimes by bronchitis orbronchopneumonia

c. Carbon dioxide (CO2)- breathing air with more than 30% CO2 can quickly induce unconsciousness

and cause death

- Air with 5% CO2: perceptible increased respiration; 6-10%: shortness ofbreath, headaches, dizziness, sweating, and general restlessness; 10-15%:

impaired coordination and abrupt muscle contractions; 20-30%: loss of consciousness and convulsions; over30%: can cause death

d. Hydrogen Chloride (HCl)- irritates mucous membranes of the eyes and respiratory tract- conc. over 35 ppm: cause irritation of the throat after short exposure; >100

ppm: pulmonary edema, and often laryngeal spasm

e. Hydrogen Fluoride (HF)- poisoning (exceeds 250 ppm), conjunctivitis, skin irritation, bone

degeneration and mottling of teeth- excess fluorine causes fluorisis, an affliction that eventually kills animals by

destroying their bonescbd ntr / geology 11 lecture / july 2002


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VOLCANISM

2. Lahar- an Indonesian term that describes a hot or cold mixture of water and rock

fragments flowing down the slopes of a volcano and (or) river valleys- when moving, a lahar looks like a mass of wet concrete that carries rock

debris ranging in size from clay to boulders more than 10 m in diameter- formed by intense rainfall during or after an eruption--rainwater can easily

erode loose volcanic rock and soil on hillsides and in river valleys- begin as landslides of saturated and hydrothermally altered rock on the flank

of a volcano or adjacent hillslopes

Effects:a. economic and environmental damageb. severe flooding and extremely high rates of sedimentation

3. Volcano landslides- large masses of rock and soil that fall, slide, or flow very rapidly under the

force of gravity

factors triggering landslides: intrusion of magma into a volcano explosive eruptions large earthquake directly beneath a volcano or nearby

intense rainfall

Effects:

explosive eruptions; buried river valleys with tens of meters of rock debris; lahars;triggered waves and tsunamis, and created deep horseshoe-shaped craters

4. Lava flows- streams of molten rock that pour or ooze from an erupting vent

Effects:a. explosions when lava interacts with water, the collapse of an active lavadelta, asphyxiation due to accompanying toxic gases, pyroclastic flows from acollapsing dome, and lahars from meltwater

b. buried homes and agricultural land under tens of meters of hardened blackrock

5. Pyroclastic flows

- high-density mixtures of hot, dry rock fragments and hot gases that moveaway from the vent that erupted them at high speeds



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VOLCANISM

Effects:a. shattered and buried objects/structuresb. the extreme temperatures (200C and 700C) can cause combustiblematerial to burn, especially petroleum products, wood, vegetation, and houses

6. Tephra

- general term for fragments of volcanic rock and lava regardless of size thatare blasted into the air by explosions or carried upward by hot gases in eruptioncolumns or lava fountains

Effects:a. disruptive to economic activityb. can obscure sunlight: temporary darkness and reduce visibility to zeroc. impassable roads, highways, and airport runwaysd. infrastructure damages

GEOTHERMAL ENERGY

Geothermal energy is produced by tapping naturally occurring steam and hot waterlocated beneath the surface in regions where subsurface temperatures are highdue to relatively recent volcanic activity.

Geothermal power plants - use wells to pipe steam and hot water trappedunderground to the surface to make electricity

Geysers Power Plant, California- the world's largest geothermal power plant

FORMSOF GEOTHERMAL RESOURCES

A. Hydrothermal Reservoirs- large pools of steam or hot water trapped in porous rocks- dry steam, high-temperature hot water (flash technology), moderate-temperature hot water (binary cycle)

B. Earth Energy- heat + "direct-use" technologies such as geothermal heat pumps (GHP) anddistrict heating systems

Geothermal heat pumps - GHPs use the Earth's relatively constant groundtemperature to provide low-cost heating and cooling.

District heating systems circulation of hot water through pipes

OTHER FORMSOF GEOTHERMAL ENERGYa. Hot dry rock



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VOLCANISM

b. Magmac. Geopressured brines - contain dissolved methaneFAVORABLEGEOLOGICALFACTORSFORAGEOTHERMALRESERVOIROFCOMMERCIALVALUE:

a. potent source of heatb. large, porous reservoirs with channels connected to the heat sourcec. capping rocks of low permeability that inhibit the flow of water and heat

Steam (high T): drive turbines and generate electrical power(low T): fluids provide hot water for space-heating purposes, heat for

greenhouses and industrial uses, and hot or warm springs at resort spas

BENEFITSFROM GEOTHERMAL ENERGY

Environment - Geothermal energy offers an environmentally benign source ofelectricity. Geothermal power plants meet the most stringent environmental

regulations and release little, if any, carbon dioxide, a greenhouse gas suspected ofcontributing to global warming.

Reliability - Geothermal power plants are highly reliably and can operate 24 hours aday. Most power plants operate more than 95 percent of the time.

Domestic resource - Geothermal energy offers a large source of secure, domesticenergy.

GEOTHERMAL ENERGYINTHE PHILIPPINES(www.energy.com.ph)

PNOC Energy Development Corporation (EDC) - established in 1976 toundertake exploration and development of geothermal energy sources in thecountry

- engaged in integrated power generation and the sale of steam to theNational Power Corporation (NPC)

- responsible for making the Philippines the 2nd largest producer ofgeothermal steam and user of wet steam technology of energy production.

- to date, it operates nine (9) geothermal steamfields with an aggregatecapacity of 1,145 megawatts (~60% of the country's total installed geothermalcapacity)

- presently operates four power plants, which were built through theBuild-Operate -Transfer scheme

- continues to place the utmost emphasis on operational safety followingthe International Safety Rating system (ISRS) in all its production fields. The

http://www.napocor.com.ph/http://www.napocor.com.ph/


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VOLCANISM

ISRS is an effective management tool used by companies worldwide to ensureoperational safety

Geothermal

Steamfield

Installed

Capacity(MW)

Powerplant Owner

orBOT partner*

Commissioning

Date

Bacon-Manito (Luzon)

BacMan I 110 Napocor 1993

BacMan II 40 Napocor 1995

Leyte

Tongonan IUpper MahiaoMalitbog

Optimization PlantsMahanagdong

112.5125232

50180

NapocorCalEnCalEn

CalEnOrmat

19831997

1996-1997

19971997

Palinpinon (So. Negros)

Palinpinon I 112.5 Napocor 1983

Palinpinon II 80 Napocor 1995

Mt. Apo (Mindanao)

Mindanao IMindanao II

5248

Oxbow-MarubeniOxbow-Marubeni

19971999

Geothermal Operations of the PNOC-EDC

*Under a build-operate-transfer (BOT) arrangement, PNOC-EDC jointly operates its power plants in Leyte andMindanao with foreign consortiums. After a ten-year cooperation period, these power facilities shall be turned overcompletely to PNOC-EDC.

Areas under exploration/development

PotentialCapacity

(Mwe)

CommissioningDate

Mambucal, Northern NegrosMontelago, MindoroMt. Cabalian, Southern LeyteRangas Tanawon, Sorsogon

403011020

2004*2004*2006*2007*

*tentative

http://www.energy.com.ph/BacMan.htmhttp://www.energy.com.ph/Leyte.htmhttp://www.energy.com.ph/Southern%20Negros.htmhttp://www.energy.com.ph/Mt.%20Apo.htmhttp://www.energy.com.ph/BacMan.htmhttp://www.energy.com.ph/Leyte.htmhttp://www.energy.com.ph/Southern%20Negros.htmhttp://www.energy.com.ph/Mt.%20Apo.htm

lec5-volcanism

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