Volcanoes

Shield Volcanoes

Broad, dome-shaped with gentle slopes; like a warrior's shield.

Shield Volcanoes

Built by low-viscosity basaltic lava

flows.

Shield Volcanoes

Some of the largest volcanoes in the

world are shield volcanoes.

Shield Volcanoes

Eruptions are effusive and lava flows

can travel long distances

Composite Volcanoes (Stratovolcanoes)

Steep-sided and has a conical shape.

Composite Volcanoes (Stratovolcanoes)

• Built up by many layers of hardened lava,

tephra, pumice, and volcanic ash.

Composite Volcanoes (Stratovolcanoes)

Intermediate viscosity magma.

Composite Volcanoes (Stratovolcanoes)

Eruptions are explosive; alternating lava

flows and pyroclastic materials.

Calderas

Large, basin-like depressions

Calderas

• Formed by the collapse of a volcano

following a major eruption.

Calderas

• Range in form and size from roughly

circular depressions 1.5 to 24 km in

diameter to huge elongated

depressions as much as 100 km

long.

Calderas

• Eruptions are cataclysmic

Cinder Cones

• Small (tens to hundreds of meters

tall) and has a steep slope and a

bowl-shaped crater.

Cinder Cones

• Built from loose pyroclastic

fragments.

Cinder Cones

• Eruptions are moderately explosive

and short-lived.

Cinder Cones

• Commonly found on flanks of larger

volcanoes

Lava Domes (Volcanic Domes)

• Steep-sided and dome-shaped.

Lava Domes (Volcanic Domes)

• Some domes form craggy knobs or

spines over the volcanic vent,

whereas others form short, steep-

sided lava flows known as

"coulees.“

Lava Domes (Volcanic Domes)

• Formed by relatively small, bulbous

masses of high-viscosity lava;

consequently, on extrusion, the lava

piles over and around its vent.

Lava Domes (Volcanic Domes)

• Often preceded or followed by

explosive eruptions

Icelandic type

• Effusions of molten basaltic lava that flow from long, parallel fissures; creates flood basalts.

Icelandic

• Effusive eruption; low gas content.

Vulcanian type

• Short and violent forming

vigorous eruption columns

of highly fragmented ash.

Vulcanian type

• Small volumes of magma

with large blocks and

bombs.

Vulcanian type

• Explosive eruptions; magma

plugs are violently expelled.

Hawaiian type

• Lava flows from the vent or fissures

in a relatively gentle, low-level

eruption.

Hawaiian type

• Fluid low-viscosity, low gas content

but high temperature basaltic lavas;

minimal amount of ash.

Hawaiian type

• Forms lava fountains, lava lakes, and

shield volcanoes.

Hawaiian type

• Effusive eruptions; occasional mild

explosivity.

Strombolian type

• Short-lived and

explosive eruptions of

gas and lava; ejects

bombs and lapilli.

Strombolian type

• Form cinder cones.

Strombolian type

• Explosive (moderately)

eruptions; intermittent

eruptions caused by gas

bubble bursts.

Pelean type

• Viscous magma forming

lava domes; often forms

large eruptive columns.

Pelean type

• Dome collapse triggers

pyroclastic flows (nuée

ardente).

Pelean type

• Explosive eruptions;

dome growth and

collapse.

Plinian/Vesuvian type

• Sustained, violent eruptions with tall

eruption columns (20–40 km)

Plinian/Vesuvian type

• Widespread ashfall, pyroclastic flows,

pumice rain

Plinian/Vesuvian type

• High gas content, rhyolitic to dacitic

magma

Plinian/Vesuvian type

• Catastrophic and (highly) explosive

eruptions; can lead to caldera formation.

Ultra-Plinian type

• Largest of all volcanic eruptions; extremely

explosive eruptions.

Ultra-Plinian type

• Thick pyroclastic flows that cover vast

areas and may produce widespread ash-

fall deposits.

Ultra-Plinian type

• Large calderas form above vacated magma

chambers.

Ultra-Plinian type

• The term "Ultraplinian" is used informally

or descriptively to characterize the most

powerful Plinian-type eruptions—those at

the upper end of VEI 6 or into VEI 7.

phreatic volcanic eruptions

only blast out fragments of pre-

existing solid rock from the volcanic

conduit; no new magma is erupted

Surtseyan

- caused by the interactions between shallow water and lava

Lava flows

- streams of molten rock that pour or ooze

from an erupting vent. Lava is erupted during

either nonexplosive activity or explosive lava

fountains

Aa

- rough or rubbly surface composed of

broken lava blocks called clinker

- usually of higher viscosity than

pāhoehoe

- typically erupt at temperatures of

1000 to 1100°C

Pahoehoe

- smooth, billowy, undulating, or ropy

surface

- typically have a temperature of 1100

to 1200 °C

Volcanic ash

- mixture of rock, mineral, and glass

particles expelled from a volcano

during a volcanic eruption.

Volcanic ash

- The particles are very small—less

than two millimeters in diameter.

They tend to be pitted and full of

holes, which gives them a low

density

Tephra fall

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

erupted during either nonexplosive activity or explosive lava fountains.

Pyroclastic flow

- a fast-moving current of superheated

gas (~1,000°C) and tephra, which

reaches speeds of up to 700 km/h

Pyroclastic flow

- a higher proportion of gas to rock

ratio (lower density) makes it more

turbulent to form pyroclastic (or base)

surges

Volcanic bombs

- formed when a volcano ejects

viscous fragments of lava during an

eruption and can be thrown many

meters to kilometers from an

erupting vent.

Volcanic bombs

- can cause severe injuries and death

to people in an eruption zone.

Volcanic gases

- include gases trapped in cavities (vesicles) in volcanic rocks, dissolved

or dissociated gases in magma and lava, or gases emanating directly

from lava

Volcanic gases

- or indirectly through groundwater heated by volcanic action

Debris avalanches

- Very high-velocity flows of large-

volume mixtures of rock and

regolith that result from a complete

collapse of a mountainous slope.

Debris avalanches

- Often triggered by volcanic

eruptions and earthquakes

Lahars

- Hot or cold mixture of water and

rock fragments that flows down the

slopes of a volcano and typically

enters a river valley.

Lahars

- Small seasonal events are

sometimes referred to as "debris

flows“.