Styles of EruptionsStyles of Eruptionsandand

Volcanic Hazards Volcanic Hazards

Styles of volcanic Styles of volcanic eruptions eruptions

Some volcanoes may erupt only once Some volcanoes may erupt only once - - monogeneticmonogenetic (Diamond Head) (Diamond Head)

Other volcanoes erupt many times - Other volcanoes erupt many times - polygeneticpolygenetic (Kilauea) (Kilauea)

Some erupt very gently (Kilauea)Some erupt very gently (Kilauea) Others are very violent and explosive Others are very violent and explosive

(Mt. St. Helens, Mt. Pinatubo)(Mt. St. Helens, Mt. Pinatubo) How come?How come?

Explosive volcanoes found Explosive volcanoes found associated with subduction associated with subduction

zoneszones Explosiveness is a function of magma Explosiveness is a function of magma

viscosity viscosity (resistance to flow)(resistance to flow) Magmas that generate the explosive Magmas that generate the explosive

volcanoes are much more viscous volcanoes are much more viscous than the non-explosive magmasthan the non-explosive magmas More silica, cooler magma, more gasMore silica, cooler magma, more gas

Hawaiian magmasHawaiian magmas

Not very explosiveNot very explosive Not very viscousNot very viscous

Low silica, hot magma, moderate gas contentLow silica, hot magma, moderate gas content

Eruptive styles areEruptive styles are

Classified by level of eruption Classified by level of eruption explosivenessexplosiveness

I. Flood eruptions I. Flood eruptions

Least explosive eruptions Least explosive eruptions Very fluid basalt erupted in very large Very fluid basalt erupted in very large

quantities quantities VERY FASTVERY FAST Lavas erupted over large areasLavas erupted over large areas Thought to develop as hot spots burn Thought to develop as hot spots burn

thru crustthru crust

Columbia

Plateau More than

420,000 cubic km of lava

Flood basalts

II. Hawaiian-type eruptions

Hawaiian-type eruptions Hawaiian-type eruptions

The next least explosive kind of The next least explosive kind of eruptioneruption

Fluid magmas with small amounts of Fluid magmas with small amounts of gasgas

Eruptions relatively gentleEruptions relatively gentle Periodically have a violent eruption but Periodically have a violent eruption but

very rare - very rare - Drive in volcanoesDrive in volcanoes

Hawaiian-type eruptions Build shield volcanoes

Styles of explosive volcanismStyles of explosive volcanism

VulcanianStrombolian VulcanianStrombolian

SurtseyanSurtseyan phreatoplinianphreatoplinian

Peléan PeléanPlinianPlinian

Intensity (dispersal)

Fra

gm

enta

tio

n (

gra

in s

ize)

Modified from Julia Sable

III. Strombolian eruptionsIII. Strombolian eruptions

Named for volcanic island off coast of ItalyNamed for volcanic island off coast of Italy Characterized by less fluid lavasCharacterized by less fluid lavas Moderate explosive activityModerate explosive activity Tephra commonTephra common Lots of ash blankets country sideLots of ash blankets country side Basalt and andesite common Basalt and andesite common Large steep-sided composite volcanoes built by Large steep-sided composite volcanoes built by

repeated Strombolian eruptionsrepeated Strombolian eruptions

More explosive eruptionsBuild composite cones

Mt. Shasta, California

‘A’a flows

IV. Vulcanian eruptionsIV. Vulcanian eruptions

Characterized by more viscous lavasCharacterized by more viscous lavas ““Stubbly” flows are common Stubbly” flows are common Lots of ashLots of ash Andesite most commonAndesite most common

Arenal Volcano, Costa Rica

V. Peléan eruptionsV. Peléan eruptions

Named for 1902 eruptions of Mount Named for 1902 eruptions of Mount Pelée on Martinique in the Pelée on Martinique in the CaribbeanCaribbean

Mt. PeléMt. Peléeruptioneruption

Almost Almost 30,000 30,000 people people were killed were killed instantlyinstantly

Peléan eruptionsPeléan eruptions

Lavas highly viscous, very explosive Lavas highly viscous, very explosive Explosive eruption of highly gas-charged Explosive eruption of highly gas-charged

lava leads to lava leads to nuée ardentenuée ardente (glowing (glowing avalanche) or avalanche) or pyroclastic flow pyroclastic flow which which move at move at 60+ kph60+ kph and are and are 300300degdeg C C inside inside

Don’t outrun these guys!!!Don’t outrun these guys!!!

Pyroclastic flows formed during 1968 eruption of Mt. Mayon

Ash cloud is 30,000 fthigh

Flows caused by ash cloud collapse or lava dome collapse

VI. Plinian EruptionVI. Plinian Eruption most powerful eruptionmost powerful eruption

Named for Roman naturalist killed in Named for Roman naturalist killed in explosion of Mt. Vesuvius in 79 A.D explosion of Mt. Vesuvius in 79 A.D

VeryVery destructive destructive Accompanied by major collapseAccompanied by major collapse

Plinian EruptionPlinian Eruption

Mt. St. Helens is good exampleMt. St. Helens is good example

before during

Plinian = most powerful Plinian = most powerful eruptioneruption

Crater Lake in Oregon formed by similar Crater Lake in Oregon formed by similar explosive eruptionexplosive eruption

Ash from this volcano (Mt. Mazama) Ash from this volcano (Mt. Mazama) found all over the Pacific Northwest & found all over the Pacific Northwest & as far east as the Mississippi River!as far east as the Mississippi River!

Greatest Plinian eruptions of modern Greatest Plinian eruptions of modern times: times:

1813 explosion of Tambora volcano 1813 explosion of Tambora volcano (eastern Indonesia) (eastern Indonesia)

1883 explosion of Krakatau (Sunda 1883 explosion of Krakatau (Sunda Strait between Java and Sumatra)Strait between Java and Sumatra) Explosion heard in northern Australian, Explosion heard in northern Australian,

2400 km away2400 km away

Plinian = most powerful Plinian = most powerful eruptioneruption

Other Recent EruptionsOther Recent Eruptions

PinatuboPinatubo = Vulcanian-type eruption = Vulcanian-type eruption Mt. UnzenMt. Unzen (Japan,1991) -- generated a (Japan,1991) -- generated a

number of lava domes that collapsed, number of lava domes that collapsed, sending pyroclastic flows down the side sending pyroclastic flows down the side of the volcano, so it can be classified as a of the volcano, so it can be classified as a Peléan eruptionPeléan eruption

Volcanoes & Plate TectonicsVolcanoes & Plate Tectonics

OK. So, where do you find all these OK. So, where do you find all these volcanic eruptive styles?volcanic eruptive styles?

Flood eruptionsFlood eruptions - atop hot spots - atop hot spots HawaiianHawaiian - at hot spots & along MOR - at hot spots & along MOR All the restAll the rest are associated with subduction are associated with subduction!!

Styles of explosive volcanismStyles of explosive volcanismWhat are the hazards?What are the hazards?

VulcanianStrombolian VulcanianStrombolian

SurtseyanSurtseyan phreatoplinianphreatoplinian

Peléan PeléanPlinianPlinian

Intensity (dispersal)

Fra

gm

enta

tio

n (

gra

in s

ize)

Volcanic Volcanic HazardsHazards

1. 1. LavaLava

FlowsFlows

Volcanic HazardsVolcanic Hazards

2. 2. Falling TephraFalling Tephra

Like one sees at the Like one sees at the beginning of the beginning of the movie Dante’s Peak.movie Dante’s Peak.

Falling tephra in Yakima, WashingtonFalling tephra in Yakima, Washingtonduring Mt. St. Helens eruptionduring Mt. St. Helens eruption

More Volcanic HazardsMore Volcanic Hazards

Pyroclastic flowsPyroclastic flows Mudflows - LaharsMudflows - Lahars Toxic volcanic gasesToxic volcanic gases

Hazards in HawaiiHazards in Hawaii

Lava flowsLava flows

Note: Note: The next few slides are courtesy of The next few slides are courtesy of G&G graduate student Chris GreggG&G graduate student Chris Gregg

Lava Flow Hazard Zone Map of Hawaii

Historic Eruptions

Mauna Loa:

33 flows since 1843 5 reached ocean in Kona

Hualalai:

3 flows since ~1800 2 reached ocean in Kona

High effusion rates: 3-12 x 106 m3 day -1

< 24 hours< 24 hours

Steep slopes > 6 %:

Hualalai: >50 %

Mauna Loa: 35 %

Kilauea: <5 %

Fast transit times:

Lava FlowsLava FlowsFrom Hualalai From Hualalai

and Mauna Loa and Mauna Loa That Have That Have

Affected Kailua-Affected Kailua-KonaKona1877

Hualalai’s last eruptions (c. 1800-Hualalai’s last eruptions (c. 1800-1801)1801)

Subdivision

Airport

Resorts

MAUNA LOA’s Radial Vents (33) and Rift Zones

Historic radial vent eruptions: 1843, 1859, 1877, 1935

Typical Mauna Loa Eruptions:

Summit followed by fissure eruptions

What Controls the Flow Paths of Lava Flows? Topography

What Controls the Speed of

Lava Flows? Slope angle, surface roughness, eruption rate, lava type (viscosity)

1950 Eruption:

Flow velocities 16-48 km/hr

Note that all of these hazards are associated with the big island! How come?

Worst volcanic hazards Worst volcanic hazards often occur after major often occur after major

eruptions eruptions Ash covers sides of volcano Ash covers sides of volcano Ash becomes unstable during heavy Ash becomes unstable during heavy

rainrain Ash mud flow - Ash mud flow - LAHARSLAHARS 10 years+ after Pinatubo eruption, 10 years+ after Pinatubo eruption,

mudflows were still killing peoplemudflows were still killing people

LAHAR - ASH MUD FLOWLAHAR - ASH MUD FLOWLAHAR - ASH MUD FLOW

Volcanic gasesVolcanic gases

Very dangerous Very dangerous COCO22, CO,, CO, SO SO22, H, H22S, HCl and HFS, HCl and HF

Hawaiian volcanoesHawaiian volcanoes

Do not usually emit enough gas to Do not usually emit enough gas to harm peopleharm people

Except for Except for VogVog which forms as which forms as volcano erupts and as lava enters the volcano erupts and as lava enters the ocean (Even reaches O`ahu with ocean (Even reaches O`ahu with Kona wind)Kona wind)

Attempts to control flowsAttempts to control flows

In the past, people have tried to control, In the past, people have tried to control, direct lava flows by:direct lava flows by: Diverting the flow with Diverting the flow with barriersbarriers built with built with

bulldozersbulldozers Diverting by Diverting by bombingbombing one or all of the one or all of the

following locations - the vent, edge of a flow, following locations - the vent, edge of a flow, tube entrancetube entrance

WaterWater the flow front - not very successful! the flow front - not very successful!

Avoiding volcanic hazardsAvoiding volcanic hazards

Predict themPredict them Volcanologists getting good at predicting Volcanologists getting good at predicting

eruptions of dangerous volcanoeseruptions of dangerous volcanoes Mt. St. Helens, Unzen and PinatuboMt. St. Helens, Unzen and Pinatubo But, missed 1993 Mayon eruption But, missed 1993 Mayon eruption

Predictions eruptionsPredictions eruptions Mostly made based on Mostly made based on monitoringmonitoring::

Seismic activity increasesSeismic activity increases Ground tiltingGround tilting Increased heat flowIncreased heat flow Increase in %sulfur in volcanic gasIncrease in %sulfur in volcanic gas

Because magma is moving into Because magma is moving into shallow levels under volcano!shallow levels under volcano!

Cyclic nature of Kilauea eruptions

Wai`anae Volcano

Ko`olau Volcano

Thurston Lava Tube

Meteorites have struck the Earth in the past.

Many meteorites are made of iron and nickel.

We think this represents material of planets similar to Earth.Earth’s interior (core) is probably also composed of iron and nickel.

The end!The end!