VOLCANIC ACTIVITYVOLCANIC ACTIVITY volcanismvolcanism = any activity that includes movement of magma = any activity that includes movement of magma

toward or onto surfacetoward or onto surface

volcanologistsvolcanologists = scientists who study volcanoes = scientists who study volcanoes- also called vulcanist- also called vulcanist

magmamagma = mixture of molten rock, suspended mineral grains, = mixture of molten rock, suspended mineral grains, and dissolved gases deep below surface and dissolved gases deep below surface

1. pockets grow due to melting of surrounding rock due to high 1. pockets grow due to melting of surrounding rock due to high temperatures (800temperatures (800ooC – 1200C – 1200ooC)C)

2. will expand pushing upward into crust due to being less 2. will expand pushing upward into crust due to being less densedense

3. slowly rises forcing its way 3. slowly rises forcing its way into cracks of overlying rockinto cracks of overlying rock

4. pressure may cause blocks to 4. pressure may cause blocks to break off and melt adding to break off and melt adding to pocketpocket a. increases as depth increasesa. increases as depth increases b. as pressure increases, b. as pressure increases, temperature at which a temperature at which a substance melts also substance melts also increasesincreases

5. presence of water influences whether rock will melt5. presence of water influences whether rock will melt a. at any given pressure, wet mineral or rock will melt at a. at any given pressure, wet mineral or rock will melt at

lower temperatures than same rock under dry lower temperatures than same rock under dry conditions conditions

6. viscosity depends on both temperature and composition6. viscosity depends on both temperature and composition a. hotter the temperatures, lower the viscositya. hotter the temperatures, lower the viscosity b. as amount of silica increases, viscosity increasesb. as amount of silica increases, viscosity increases7. can break through onto surface where becomes 7. can break through onto surface where becomes lavalava = =

magma that erupts onto earth’s surfacemagma that erupts onto earth’s surface

TYPES OF MAGMATYPES OF MAGMA1. 1. basaltic magmabasaltic magma (mafic) = same composition as basalt rock (mafic) = same composition as basalt rock a. forms when upper mantle meltsa. forms when upper mantle melts b. most rises rapidly to surfaceb. most rises rapidly to surface c. reacts very little with crustal rocks due to low viscosityc. reacts very little with crustal rocks due to low viscosity d. has small amounts of dissolved gases and silicad. has small amounts of dissolved gases and silica e. these volcanoes erupt relatively quietlye. these volcanoes erupt relatively quietly f. tends to form at rifts and oceanic hot spotsf. tends to form at rifts and oceanic hot spots

2. 2. andesitic magmaandesitic magma (intermediate) = same composition as (intermediate) = same composition as andesite rockandesite rock

a. found along continental margins where ocean crust is a. found along continental margins where ocean crust is subducted into mantle (subduction boundaries)subducted into mantle (subduction boundaries)

b. source material is ocean crust or oceanic sedimentsb. source material is ocean crust or oceanic sediments c. has 60% silica which results in intermediate viscosityc. has 60% silica which results in intermediate viscosity d. volcanoes will have intermediate eruptionsd. volcanoes will have intermediate eruptions

3. 3. rhyolitic magmarhyolitic magma (felsic) = same composition as granite rock (felsic) = same composition as granite rock a. forms when molten material rises & mixes with overlying a. forms when molten material rises & mixes with overlying

silica and water-rich continental crustsilica and water-rich continental crust b. high viscosity inhibits movementb. high viscosity inhibits movement c. contains about 70% silica; contains large volumes of c. contains about 70% silica; contains large volumes of

trapped gasestrapped gases d. these volcanoes are very explosived. these volcanoes are very explosive e. tend to form where hot spots underlie continental platese. tend to form where hot spots underlie continental plates

VOLCANIC ERUPTIONSVOLCANIC ERUPTIONS1. 1. lavalava = primarily molten rock but can differ in composition to = primarily molten rock but can differ in composition to

that of magma that of magma a. material can be removed or added as magma rises to a. material can be removed or added as magma rises to

surfacesurface2. types of lava:2. types of lava: a. a. mafic lavamafic lava (basaltic) = dark colored, rich in magnesium (basaltic) = dark colored, rich in magnesium

and iron and iron 1) usually of oceanic crust origin1) usually of oceanic crust origin 2) very hot and thin so flows almost like water; less 2) very hot and thin so flows almost like water; less

explosive eruptionsexplosive eruptions 3) 3) pahoehoepahoehoe = solidified = solidified

mafic lava with a mafic lava with a wrinkled surfacewrinkled surface

4) 4) aaaa = jagged chunks of lava form by rapid cooling on = jagged chunks of lava form by rapid cooling on surface of a lava flow surface of a lava flow

5) 5) pillow lavapillow lava = flows out of fissures on ocean floor and = flows out of fissures on ocean floor and cools rapidly in rounded shapes cools rapidly in rounded shapes

6) outer part of lava flow can cool so rapidly to form a 6) outer part of lava flow can cool so rapidly to form a hardened shell around liquid interior which leaves hardened shell around liquid interior which leaves tunnels in the hardened shelltunnels in the hardened shell

b. b. felsic lavafelsic lava = a lot of silica with less iron and magnesium = a lot of silica with less iron and magnesium 1) usually from melted continental crust1) usually from melted continental crust 2) cooler and thicker2) cooler and thicker

3. composition of lava that reaches the surface determines the 3. composition of lava that reaches the surface determines the force of eruptionforce of eruption

a. amount of water vapor and other gases that are a. amount of water vapor and other gases that are trapped trapped in magmain magma

b. whether it is mafic or felsic lavab. whether it is mafic or felsic lava4. types4. types a. a. quietquiet 1) due to mafic lava1) due to mafic lava 2) gases can easily escape 2) gases can easily escape 3) lava pours from volcanic 3) lava pours from volcanic

vents and runs down vents and runs down the side of the volcanothe side of the volcano

4) form volcanoes over hot 4) form volcanoes over hot spots and flow from spots and flow from rift zones on ocean floorrift zones on ocean floor

b. b. explosiveexplosive 1) usually due to felsic lava1) usually due to felsic lava

2) contain large amounts of trapped gases (mostly CO2) contain large amounts of trapped gases (mostly CO22 and H and H22O vapor)O vapor)

3) when a vent or fissure opens up, pressure is reduced3) when a vent or fissure opens up, pressure is reduced 4) dissolved gases within lava boil out explosively4) dissolved gases within lava boil out explosively 5) this sends molten and solid particles shooting 5) this sends molten and solid particles shooting into into

the the air air

Rock Formations Created:Rock Formations Created:intrusionsintrusions = underground rock masses = underground rock masses1. 1. plutonsplutons = intrusive igneous rock body exposed at surface = intrusive igneous rock body exposed at surface

due to uplift and erosion; classified by size, shape, and due to uplift and erosion; classified by size, shape, and relationship to surrounding rocksrelationship to surrounding rocks

2. 2. batholithsbatholiths = mostly composed of granite, but can have = mostly composed of granite, but can have gabbro and diorite gabbro and diorite

a. largest intrusions, can cover 100 kma. largest intrusions, can cover 100 km22

b. can reach depth of several thousand metersb. can reach depth of several thousand meters c. form core of many mountain rangesc. form core of many mountain ranges d. some are exposed at Earth’s surface due to erosiond. some are exposed at Earth’s surface due to erosion

Ex: granite domes of Yosemite National ParkEx: granite domes of Yosemite National Park Stone Mountain - Elkin, NCStone Mountain - Elkin, NC

3. 3. stockstock = similar to a batholith but covers less than 100 km = similar to a batholith but covers less than 100 km22

4. 4. laccolithlaccolith = intrusion that pushes overlying rock layers into an = intrusion that pushes overlying rock layers into an arcarc

a. have round top and flat bottoma. have round top and flat bottom b. frequently found in groupsb. frequently found in groups c. may form small dome shaped mountainsc. may form small dome shaped mountains

Ex: Black Hills, SDEx: Black Hills, SD

5. 5. sillsill = sheet of hardened magma that forms between and = sheet of hardened magma that forms between and parallel to layers of rock parallel to layers of rock

a. vary in thicknessa. vary in thickness b. can extend laterally for several kmb. can extend laterally for several km6. 6. dikedike = intrusion that cuts across preexisting rock layers = intrusion that cuts across preexisting rock layers a. may follow vertical fractures or create new onesa. may follow vertical fractures or create new ones b. can be few centimeters to several meters wide and up to b. can be few centimeters to several meters wide and up to

several km wideseveral km wide c. common in areas of volcanic activityc. common in areas of volcanic activity

extrusionsextrusions = surface rock masses and features = surface rock masses and features1. 1. volcanovolcano = cone of rock surrounding a central vent = cone of rock surrounding a central vent

through which lava flows through which lava flows2. 2. volcanic neckvolcanic neck = solidified central vent of a volcano = solidified central vent of a volcano a. forms when erosion carries away parts of the conea. forms when erosion carries away parts of the cone b. resistant to erosionb. resistant to erosion

3. 3. lava plateaulava plateau = raised, flat topped areas made of layers = raised, flat topped areas made of layers of hardened lavaof hardened lava

a. develops from lava that flows from long cracks in a. develops from lava that flows from long cracks in surfacesurface

b. covers large area filling in valleys and covering hillsb. covers large area filling in valleys and covering hills c. usually forms from basaltic lavac. usually forms from basaltic lava

Volcano AnatomyVolcano Anatomy1. 1. ventvent = opening through which magma/lava flows onto the = opening through which magma/lava flows onto the

surface surface2. 2. volcanovolcano = vent and volcanic materials that builds up on = vent and volcanic materials that builds up on

surfacesurface a. most are now dormanta. most are now dormant b. still more than 600 activeb. still more than 600 active c. spew smoke, steam, ash, cinders, and flows of c. spew smoke, steam, ash, cinders, and flows of lavalava

3. 3. craterscraters = funnel shaped pit at the top of volcanic vent = funnel shaped pit at the top of volcanic vent a. from where material is blown out of volcano by a. from where material is blown out of volcano by

explosionsexplosions b. becomes wider as magma melts and breaks down wallsb. becomes wider as magma melts and breaks down walls c. can have a smaller cone form within craterc. can have a smaller cone form within crater d. usually less than 1 km in diameterd. usually less than 1 km in diameter

4. 4. calderacaldera = large, basin shaped depression = large, basin shaped depression a. forms when magma chamber is emptieda. forms when magma chamber is emptied b. cone may collapseb. cone may collapse c. can be up to 50 km in diameterc. can be up to 50 km in diameter

Ex: Krakatau (volcanic island in Indonesia); Ex: Krakatau (volcanic island in Indonesia); Crater Lake, ORCrater Lake, OR

Kaguyak volcano, Alaska

TYPES OF VOLCANOESTYPES OF VOLCANOES1. 1. shield volcanoesshield volcanoes = form from basaltic(mafic) lava = form from basaltic(mafic) lava a. quiet eruptions spread lava out in flat layersa. quiet eruptions spread lava out in flat layers b. mountain with broad, gently sloping sides & nearly circular b. mountain with broad, gently sloping sides & nearly circular

basebase c. less explosive eruptionsc. less explosive eruptions

Ex: Mauna Loa in the Hawaiian IslandsEx: Mauna Loa in the Hawaiian Islands

2. 2. cinder cone volcanoescinder cone volcanoes = formed from explosive = formed from explosive eruptions eruptions

a. made of solid fragments ejected into air which falls a. made of solid fragments ejected into air which falls back to surface & piles up around ventback to surface & piles up around vent

b. have very steep sides (close to 40b. have very steep sides (close to 40oo)) c. rarely more than a few hundred meters highc. rarely more than a few hundred meters high

Ex: Mt. Pelee - MartiniqueEx: Mt. Pelee - Martinique Paricutin - MexicoParicutin - Mexico

3. 3. composite volcanoescomposite volcanoes = formed from both quiets = formed from both quiets and explosive eruptions and explosive eruptions

a. cone is formed mainly by lava flows from quiet eruptionsa. cone is formed mainly by lava flows from quiet eruptions 1) explosive eruptions deposit large amounts of tephra 1) explosive eruptions deposit large amounts of tephra

around vent around vent 2) after many alternating eruptions a large cone forms2) after many alternating eruptions a large cone forms 3) also known as 3) also known as stratovolcanoesstratovolcanoes which often which often

develop into high volcanic mountains develop into high volcanic mountains

Mt. St. Helen’s

b. can see bulge on face of mountain grow, see small eruption b. can see bulge on face of mountain grow, see small eruption of steam and ashof steam and ash

c. eventually, earthquake can burst bulge that has been c. eventually, earthquake can burst bulge that has been formingforming

d. can create a d. can create a laharlahar = fast moving mudflow of hot ash mixed = fast moving mudflow of hot ash mixed with snow and ice on mountain with snow and ice on mountain

e. after violent eruption, can remain relatively quiet for long e. after violent eruption, can remain relatively quiet for long period of time; but below surface magma may be building up period of time; but below surface magma may be building up pressure once againpressure once again

f. found mostly at convergent plate boundaries above f. found mostly at convergent plate boundaries above subduction zonessubduction zones

Ex: Mt. Saint Helens - WashingtonEx: Mt. Saint Helens - Washington Mt. Vesuvius - ItalyMt. Vesuvius - Italy

VOLCANIC ROCK FRAGMENTSVOLCANIC ROCK FRAGMENTS1. 1. tephra tephra (pyroclastic material) = rock fragments ejected (pyroclastic material) = rock fragments ejected a. some forms when cooling magma breaks into fragments a. some forms when cooling magma breaks into fragments

due to rapidly expanding gasesdue to rapidly expanding gases b. some forms when a spray of lava cools and solidifies as it b. some forms when a spray of lava cools and solidifies as it

flies through the airflies through the air

2. types:2. types: a. a. volcanic dustvolcanic dust = smallest particles = smallest particles 1) very fine1) very fine 2) less than 0.25 mm in diameter2) less than 0.25 mm in diameter b. b. volcanic ashvolcanic ash = particles more than 0.25 mm but less than = particles more than 0.25 mm but less than

2 mm in diameter2 mm in diameter 1) about the size of rice grains1) about the size of rice grains 2) will fall to Earth’s surface and eventually form rock2) will fall to Earth’s surface and eventually form rock 3) can be carried by the wind for great distances3) can be carried by the wind for great distances

c. c. lapillilapilli = particles more than 2 mm but less than 64 mm in = particles more than 2 mm but less than 64 mm in diameter diameter

1) generally fall near the vent1) generally fall near the vent 2) 2) cinderscinders = volcanic bombs about the size of a golf ball = volcanic bombs about the size of a golf balld. d. volcanic bombsvolcanic bombs = few centimeters to several meters in = few centimeters to several meters in

diameterdiameter 1) large clots of lava that spin through air, cooling and 1) large clots of lava that spin through air, cooling and

develop a round or spindle shape develop a round or spindle shape 2) have masses of several metric tons2) have masses of several metric tons

e. e. volcanic blocksvolcanic blocks = largest tephra = largest tephra 1) solid rock blasted from the fissure1) solid rock blasted from the fissure 2) can be as big as houses2) can be as big as houses3. 3. pyroclastic flowspyroclastic flows = rapidly moving clouds of gas, ash, and = rapidly moving clouds of gas, ash, and

other tephra down a slope other tephra down a slope a. can travels at speeds up to 200 km/ha. can travels at speeds up to 200 km/h b. contain hot, poisonous gasesb. contain hot, poisonous gases

MAJOR VOLCANIC ZONESMAJOR VOLCANIC ZONES1. subduction zones (convergent boundaries) [about 80%]1. subduction zones (convergent boundaries) [about 80%] a. ocean-continental plates collidea. ocean-continental plates collide 1) deep trench forms on ocean floor1) deep trench forms on ocean floor 2) line of volcanic mountains form along edge of continent2) line of volcanic mountains form along edge of continent 3) major active area is Pacific Ring of Fire 3) major active area is Pacific Ring of Fire

(Circum-Pacific Belt) (Circum-Pacific Belt) b. two ocean platesb. two ocean plates 1) deep trench formed1) deep trench formed 2) line of volcanic islands 2) line of volcanic islands

form along trench = form along trench = island arcsisland arcs

2. mid-ocean ridges (divergent boundaries)2. mid-ocean ridges (divergent boundaries) a. magma rises to surface through rifts at rift zonesa. magma rises to surface through rifts at rift zones b. most eruptions go unnoticed due to below ocean surfaceb. most eruptions go unnoticed due to below ocean surface c. sometimes this can rise above sea level forming c. sometimes this can rise above sea level forming islandsislands 1) 1) fissuresfissures = cracks through which lava flows = cracks through which lava flows 2) eruption can be seen when on an island created by 2) eruption can be seen when on an island created by

ridge ridgeEx: IcelandEx: Iceland

3. 3. hot spotshot spots = areas of volcanic activity that result from plumes = areas of volcanic activity that result from plumes of hot solid material that have risen from deep within of hot solid material that have risen from deep within Earth’s mantleEarth’s mantle

a. as material rises, it melts at areas of lower pressurea. as material rises, it melts at areas of lower pressure b. appear to remain stationary; areas that rise above water b. appear to remain stationary; areas that rise above water

can form islandscan form islands

c. plate above continues to drift slowly carrying volcano on c. plate above continues to drift slowly carrying volcano on surface away which causes activity to stopsurface away which causes activity to stop

d. new volcano will begin to form in seamount chaind. new volcano will begin to form in seamount chaine. islands form in line because plate is moving over areae. islands form in line because plate is moving over area f. can form f. can form flood basaltsflood basalts = erupt from fissures and form flat = erupt from fissures and form flat

plains or plateaus rather than volcanic mountainsplains or plateaus rather than volcanic mountainsEx: Hawaiian IslandsEx: Hawaiian Islands

VOLCANIC ACTIVITYVOLCANIC ACTIVITY1. 1. activeactive = one that erupts either continually or periodically = one that erupts either continually or periodically

Ex: Lassen Peak, California; Ex: Lassen Peak, California; Mt. Saint Helens, Washington; Mt. Saint Helens, Washington; Mount Katmai, AlaskaMount Katmai, Alaska

2. 2. dormantdormant = one that has been known to erupt within = one that has been known to erupt within modern times but in now inactivemodern times but in now inactiveEx: Mount Rainier, Washington; Ex: Mount Rainier, Washington; Mount Hood, OregonMount Hood, Oregon

3. 3. extinctextinct = one that is not known to have erupted = one that is not known to have erupted within modern historywithin modern history- some of these have even proven to be - some of these have even proven to be unpredictable unpredictable

PREDICTING ERUPTIONSPREDICTING ERUPTIONS1. seismographs are used to monitor small earthquakes1. seismographs are used to monitor small earthquakes a. number of earthquakes often increase until they are a. number of earthquakes often increase until they are

continuous just before eruptioncontinuous just before eruption b. increase in strength may also be a signalb. increase in strength may also be a signal2. slight bulging of surface of volcano2. slight bulging of surface of volcano a. upward movement of magma may push surface outa. upward movement of magma may push surface out b. instruments used to measure changes in distance and b. instruments used to measure changes in distance and

tilt of ground surfacetilt of ground surface3. changes in composition of gases given off3. changes in composition of gases given off4. requires knowledge of previous eruptions4. requires knowledge of previous eruptions

EXTRATERRESTRIAL VOLCANISMEXTRATERRESTRIAL VOLCANISM1. moon1. moon a. ~15% covered with basaltic lava flowsa. ~15% covered with basaltic lava flows b. sometime in past active volcanoes were presentb. sometime in past active volcanoes were present c. radioactive elements beneath moon’s surface probably c. radioactive elements beneath moon’s surface probably

provided energy for volcanic activityprovided energy for volcanic activity2. Mars2. Mars a. has numerous shield volcanoes and volcanic featuresa. has numerous shield volcanoes and volcanic features b. Olympus Mons = largestb. Olympus Mons = largest 1) shield volcano1) shield volcano 2) rises 28 km above surface, base is 600 km across, 2) rises 28 km above surface, base is 600 km across,

caldera 70 km across caldera 70 km across(could cover the state of Colorado)(could cover the state of Colorado)

c. Martian crust does not move so c. Martian crust does not move so allow lava source for allow lava source for

millions of yearsmillions of years

3. Venus3. Venus a. has more than 1600 large volcanoes and volcanic featuresa. has more than 1600 large volcanoes and volcanic features b. has countless numbers of small volcanoesb. has countless numbers of small volcanoes c. most are shield volcanoesc. most are shield volcanoes d. may still be active which would account for extreme d. may still be active which would account for extreme

surface temperatures (860surface temperatures (860ooF)F)

4. 4. IoIo = one of Jupiter’s moons; most volcanically active place in = one of Jupiter’s moons; most volcanically active place in solar systemsolar system

a. nine active volcanoes sighteda. nine active volcanoes sighted 1) photographs and data gathered by Voyager 1 and 1) photographs and data gathered by Voyager 1 and

Voyager 2 Voyager 2 2) ejects several thousand metric tons of material each 2) ejects several thousand metric tons of material each

second second b. volcanoes appear to be more powerful than those on earthb. volcanoes appear to be more powerful than those on earth 1) volcanic material reach heights of hundreds of km1) volcanic material reach heights of hundreds of km 2) plumes shaped like giant umbrella2) plumes shaped like giant umbrella c. part’s of surface regularly move up and down by as much c. part’s of surface regularly move up and down by as much

as 100 mas 100 m d. friction resulting is due to pull of gravity of Jupiter and d. friction resulting is due to pull of gravity of Jupiter and

other moons of Jupiter which other moons of Jupiter which provides energy for volcanic provides energy for volcanic

activityactivity