volcanism - geology

Geol. 11 Volcanism & Volcanic Hazards

2nd Sem AY 2013-14 U.P. Baguio

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Volcanism and Volcanic Hazards

Geology 11 Principles of GeologyA. M. P. Tengonciang & D.D. N. javier

Department of Physical SciencesUniversity of the Philippines, Baguio

Volcanism

Encompasses all processes associated with the transfer of molten rock and gases from the interior of the Earth to its surface

Volcano an opening in the crust through which molten lava and gases erupt

Eruption when magma rises from its source or from a storage reservoir and reaches the Earths surface

Why does magma rise?

Physical properties (temperature, composition, viscosity, relative buoyancy)

Input of fresh magma into magma reservoir Pushes magma upwards

Can cause magma chamber to expand/break

Degassing Magma becomes less dense

The gas exerts pressure on overlying & surrounding rocks

Squeezed out by overlying & surrounding rocks

Eruption styles

Effusive dominated by the outpouring of lava onto the ground

http://mail.colonial.net/~rpavlik/pavlikweb/images/geohazitem_143.jpghttp://www.nrcan.gc.ca/sites/www.nrcan.gc.ca.earth-

sciences/files/images/whitehorse/images/img74.jpg

Lava fountain



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2006 effusive eruption, Mayon volcano, Albay

Eruption styles

Effusive dominated by the outpouring of lava onto the ground

Explosive fragmentation of magma caused by exsolution & expansion of magmatic gases

Eruption mechanisms

Decompression and exsolution of magmatic gas

Interaction of water with ascending magma explosive!!!

Explosivity of eruptions is affected by

Composition (silica content)

Temperature

Dissolved gases

SiO2 MAGMATYPE

TEMP. (oC) VISCOSITY GASCONTENT

ERUPTION STYLE

~50% mafic ~1100 low low nonexplosive

~60% intermediate ~1000 intermediate intermediate intermediate

~70% felsic ~800 high high explosive

Ref: http://www.geology.sdsu.edu/how_volcanoes_work/Controls.html



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Magma viscosity

Viscosity

the degree to which a substance resists flow

depends on T, composition, & gas content (H2O, CO2, SO2, H2S, SO3, CO, COS, CH4, HCl, HF, H2, O2, N2, CS2, NH4, B, Br)

In silicate magmas, SiO4

4- tends to polymerize by sharing oxygens, forming irregularly-shaped groupings

silica content, T, gas content = viscosity

http://upload.wikimedia.org/wikipedia/commons/b/b7/Viscosity.gif

Products of eruption1. Lava

Aa -characterized by a rough or rubbly surface composed of broken lava blocks called clinker

Pahoehoe -smooth, billowy, undulating, or ropy surface

Pillows

2. Pyroclastic material (Tephra)

ash (64 mm)

3. volcanic gases

water vapor, H2O

carbon dioxide, CO2sulfur dioxide, SO2 and others

Aa lava Pahoehoe lava

Pillow lava

- typically formed when lava emerges from an underwater volcanic vent or a lava flow enters the ocean

http://farm4.static.flickr.com/3154/2882768195_fefd780424_o.jpghttps://en.wikipedia.org/wiki/File:Nur05018.jpg



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Products of eruption

2. Pyroclastic material (Tephra)

ash (64 mm)

Volcanic ash shards from Mt Erebus, AntarcticaField of view = 400 microns

http://geoinfo.nmt.edu/labs/microprobe/images/bit161-big.jpg

Mount Pinatubo ash

http://volcanoes.usgs.gov/ash/build/32923351-028_large.jpghttp://www.uwec.edu/jolhm/EH2/Lennon/ash.jpg

Lapilli (also called cinders)Andesitic lapilli scoria from Mt St Helenshttp://eiu.edu/~cfrbj/parks/MSHE/lapilli.jpg



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Volcanic bombs

http://volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/30410914-028_large.JPG

Volcanic bombs are usually expelled while molten

http://www.sfll.bnu.edu.cn/default///Unit%209%20of%20HW/Volcanic%20Bombs.files/cowpieB.jpg

http://www.sfll.bnu.edu.cn/default///Unit%209%20of%20HW/Volcanic%20Bombs.files/brdcrst2.jpg

http://www.sfll.bnu.edu.cn/default///Unit%209%20of%20HW/Volcanic%20Bombs.files/fusiform3.jpg

Volcanic block- solid rock fragment greater than 64 mm in diameter that was ejected from a volcano during an explosive eruption

http://volcanoes.usgs.gov/images/pglossary/block.php http://www.volcano.si.edu

Volcanic gases

water vapor, H2O

carbon dioxide, CO2 sulfur dioxide, SO2 hydrochloric acid, HCl

hydrogen fluoride, HF

hydrogen sulfide, H2S

carbon monoxide, CO

hydrogen gas, H2 ammonia, NH3 methane, CH4 tetrafluorosilane, SiF4

Gases in Magmas

Major gases

Water vapor (H2O)

Carbon dioxide (CO2)

Nitrogen (N2)

Minor gases

Sulfur compounds (SO2, H2SO4, etc.)

Carbon monoxide (CO)

Chlorine (Cl2)

Fluorine (F2, HF)

High silica (rhyolitic) magmas generally have more gas than low silica (basaltic) magmas

H2O 67.7

CO2 12.7

N2 7.65

SO2 7.03

SO3 1.86

S2 1.04

H2 0.75

CO 0.67

Cl2 0.41

Ar 0.20

Gases from a Hawaiian volcano

Mayon releasing gas



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Volcanic landforms

1. Pyroclastic cones

Small volcanoes that grow from thousands of recurring incandescent jets made of molten-to-plastic lumps of magma (scoria, UK/cinders, US)

Form steep-sided mounds with a small summit crater

Commonly occur in clusters or on the flanks of other volcanoes (e.g. shield volcanoes)

http://www.earthonlinemedia.com/ebooks/tpe_3

e/volcanic_landforms/volcano_types_2.html

Puu Oo cinder cone

http://en.wikipedia.org/wiki/File:Puu_Oo_-_Crater_Lava_pond_1990.jpg

1946 eruption

Paricutin cinder cone, Mexico

http://en.wikipedia.org/wiki/File:Paricutin_30_612.jpg

http://en.wikipedia.org/wiki/File:Paricutin_30_613.jpg

Cinder cone in 1943

http://en.wikipedia.org/wiki/File:Paricutin.jpg

Paricutin in 1994

Sunset Crater

http://volcano.oregonstate.edu/sunset-craters

(Tarbuck, E. J., Lutgens, F.K., & Tasa, D. 2009. GEODe: Earth Science v.3)

http://taaltours.blogspot.com/

http://en.m.wikipedia.org/wiki/Tagaytay_City

Binintiang Malaki, Taal Home on a cinder cone

http://realestate.yahoo.com/promo/the-home-at-the-top-of-a-volcano.html



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Volcanic landforms

2. Composite volcanoes (aka stratovolcanoes)

Made of innumerable layers of:

pyroclastic material

lava flow deposits

rubble derived from the flow & break-up of brittle lava & dome rocks

http://web.gccaz.edu/~lnewman/gph111/topic_un

its/Igneous_Vulcanism/14_23d.jpg

Volcanic landforms

Composite volcanoes (aka stratovolcanoes)

Build a framework that support the growth of volcanoes with great heights

Most stand isolated several tens of km apart in elongate chainshttp://web.gccaz.edu/~lnewman/gph111/topic_un


Volcanic landforms

Composite volcanoes (aka stratovolcanoes)

Constructed from multiple eruptions spanning a few hundred to hundreds of thousands of years

http://web.gccaz.edu/~lnewman/gph111/topic_un


SE NW

35-4032-40

From A. Tengonciang

Klyuchevskaya volcano, Kamchatka peninsula, Russia

http://www.volcano.si.edu/volcano.cfm?vn=300260



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Mount St. Helens, Washington, USABefore and after eruption

http://www.lethist.lautre.net/mt_st_helens2.jpg

http://pubs.usgs.gov/circ/c1050/fig49.jpg

Mount St. Helens, Washington, USA before and after eruption

Volcanic landforms3. Shield volcanoes

Broad with low slopes, like overturned shields

Constructed of solidified lava that was originally very fluid, moving at speeds up to 12 km/hr

Fast lavas can flow long distances, to construct gentle slopes & broad summits, forming lava plateaus

(Tarbuck, E. J., Lutgens, F.K., & Tasa, D. 2009. GEODe: Earth Science v.3)

http://clasfaculty.ucdenver.edu/callen/1202/Battle/Build/VolcanicEx/Extrusive.html

4. Calderas

Spanish, cauldron

Large craters that form when the ground surface above a partially empty magma chamber collapses into the void

Dimensions may range from a few km to as large as 60 km in diameter

Volcanic landforms

http://en.wikipedia.org/wiki/File:Taal_Volcano_satellite_image.gif

www.volcano.si.edu

Taal Caldera Lake



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Photo credit: A. Tengonciang

Pinatubo caldera lake

http://64.19.142.11/upload.wikimedia.org/wikipedia/commons/thu

mb/1/14/Santorini_Landsat.jpg/280px-Santorini_Landsat.jpg

http://upload.wikimedia.org/wikipedia/commons/0/0c/The_Santorini_Caldera.jpg

Santorini caldera, Greece

http://en.wikipedia.org/wiki/File:Ia_Santorini-2009-1.JPG

http://www.volcano.si.edu/volcano.cfm?vn=212040

View of Santorini caldera walls

Eruption on May 27, 1883

Anak Krakatau, May 17, 1997.

Kaguyak volcano, Alaska

http://en.wikipedia.org/wiki/File:MountKaguyak.jpg

Volcanic landforms

5. Domes

Domes result from the slow extrusion of highly viscous magma

May start as highly explosive eruptions that wane into slow, viscous lava extrusion, forming thick stubby flows or bulbous domes



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Santiaguito volcanic dome complex in Santa Maria volcano, Guatemala

http://www.photovolcanica.com/VolcanoInfo/Santiaguito/Gua07_0528.jpg

http://volcanoes.usgs.gov/activity/methods/deformation/tilt/msh.php

Dome

http://en.wikipedia.org/wiki/File:PaodeAcucar.JPG

Sugarloaf Mountain, Rio de Janeiro

(granite-gneiss dome) Volcanic landforms

6. Maar

A small volcano with a wide crater of diameters ranging from several hundred meters to 1-2 km

Form from steam explosions that occur when rising magma comes into contact and mixes with groundwater or surface water

Seven Lakes of San Pablo, Laguna

http://cdn1.vtourist.com/15/5108108-the_7_lakes_San_Pablo_City.jpg

http://www.pinoymountaineer.com/2008/08/seven-lakes-of-san-pablo.html

Maar de Tazenat, Chane des Puys, France

http://dichamp.pagesperso-orange.fr/englishversion/prinvolce/tazenate.html

Mount Tabaro

http://64.19.142.12/upload.wikimedia.org/wikipedia/commons/thu

mb/a/a2/Taal_volcano_crater.jpg/300px-Taal_volcano_crater.jpg



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Volcanic landforms

7. Lava plateau (e.g. Giants Causeway , Northern Ireland)

http://matadornetwork.com/trips/60-mind-bending-rock-

formations-from-around-the-world-pics/

Flood Basalts

Large volume outpourings of basaltic magma from fissure vents

Examples: Laki (Iceland), Columbia River Plateau (Washington, Oregon), Deccan Traps (India), Siberian Traps (Russia)

Flood Basalt:Laki, Iceland, 1783

Largest basalt eruption in recorded history

Basalt erupted from a 32 km long fissure

Covered an area of 565 km2 with 13 km3 of lava.

http://64.19.142.11/images.intellicast.com/App_Images/Article/175_18.jpg

http://www.geog.cam.ac.uk/research/projects/eruptions/figures.html

Factors that determine the morphology of a volcanic feature

What is a volcanic hazard?

A volcanic hazard refers to any potentially dangerous volcanic process (e.g. lava flows, pyroclastic flows).

What is a volcanic risk?A volcanic risk is any potential loss or damage as a result of the volcanic hazard that might be incurred by persons, property, etc. or which negatively impacts the productive capacity/sustainability of a population.

Volcanic hazards video

Ash falls

Hot ash flows

Mudflows

Volcanic landslides

Volcanic tsunami

Lava flows

Volcanic gases



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Benefits of Volcanism

1. Hot springs2. Geothermal

energy3. Oxygen4. Global cooling5. Fertile soil6. Natural beauty

Hot springs and geysers

Bacon-Manito, Philippines

How do we know if a volcano is active?

Active erupted during the last 10,000 yrs.

Inactive no activity during the last 10,000 yrs.

How many volcanoes are there in the Philippines?

22 active volcanoes and more than 200 inactive

most active is Mayon Volcano with 47 historical eruptions

7 active volcanoes are being monitored by PHIVOLCS



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Global Distribution of Volcanoes

DIGIT, 2002

Some uses of igneous rocks

Basalt - road pavement

Granite and rhyolite decorative stone

Pumice - abrasives

Andesite and diorite - material for retaining walls

Obsidian ornamental stone

volcanism - geology

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