Classes of volcanoes

Add Your Title HereA volcano is a place on the Earth's surface where molten rock, gases and pyroclastic debris erupt through the earth's crust.

The most common perception of a volcano…

Volcano Classification

• shape of the volcano• the materials they are built of• the way the volcano erupts

StratovolcanoA stratovolcano is…

Composite volcanoes:

-erupt in different ways at different times

-built in layers

- quiet between eruptions

Mayon volcano, Philippines

Mount Shasta, California

Mount Shasta, California

Composite Volcanoes or Stratovolcanoes

Andesite magma, tends to form composite cones.

-crater at the summit

Lava

-through breaks in the crater wall -from fissures on the flanks of the cone

-8,000 feet above their bases

When volcanic activity ceases, erosion begins to destroy the cone.

-cone is stripped away and the hardened magma filling the conduit and fissures (the dikes) become exposed

All that is left is the plug or "volcanic neck" and dike complex projecting above the land surface

The Evolution of a Composite volcano

A. Magma, rising upward through a conduit, erupts at the Earth's surface to form a volcanic cone. Lava flows spread over the surrounding area.

B. As volcanic activity continues, the cone is built to a great height and lava flows form an extensive plateau around its base.

C. When volcanic activity ceases, erosion starts to destroy the cone. After thousands of years, the great cone is stripped away to expose the hardened "volcanic plug" in the conduit.

D. Continued erosion removes all traces of the cone and the land is worn down to a surface of low relief. All that remains is a projecting plug or "volcanic neck," a small lava-capped mesa, and vestiges of the once lofty volcano and its surrounding lava plateau.

Creation

• common at subduction zones, forming chains along plate tectonic boundaries where oceanic crust is drawn under continental crust or another oceanic plate

Composite volcanoes usually erupt in an explosive way.This is usually caoused by viscous magma.

Hazards

In recorded history, explosive eruptions at subduction zone volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, like Mount St. Helens and Mount Pinatubo, typically erupt with explosive force.

Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards.

Mount Pinatubo (June 15, 1991) located 90 km from Manila -spewed ash 40 kilometres into the air

-produced huge pyroclastic flows and mudflows that devastated a large area around the volcano

-one of the largest eruptions in the 20th Century

Eruption of Mount Pinatubo was global:

-cooler-than-usual temperature-the aerosol dispersed-droplets of sulfuric acid-0.5 °C-affect the weather for a few years

Mount

Pinatubo,

Philippines

Composite

volcano.

June 1991

Unzen Volcano (island of Kyushu about 40 km east of Nagasaki) awakened from its 200-year slumber on 3 June 1991

-pyroclastic flow killed 43 people, including three volcanologists

-one of 75 active volcanoes-1792, more than 15.000 people

Unzen eruption

Pompeii (79AD)

On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.

Pompeii (79AD)

Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings.

Pompeii (79AD)

The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire.

Different shapes of strato-volcanoes:

• concave (like Agua), • pyramidal (like Stromboli)• convex-concave (like Vesuvius), • helmet-shaped (like Mount Rainier), • collapse caldera (like Graciosa), • nested (like El Piton in Teide), • multiple summits (like Shasta), • elongated along a fissure (like Hekla).

There are many composite volcano chains on earth, notably around the Pacific rim, known as the "Rim of Fire".

Shield volcano

• Shield volcano

• Some of the largest volcanoes in the

world

• products of hotspot volcanism, but can

form at rift and subduction zones as

well

• The types of eruptions -

Hawaiian eruptions

22

Characteristics of hawaiian eruption:

• effusive emission of fluid lavas• mobile nature of these lavas

Shield volcanoes vary widely in size with their age.-often measure 5 to 6 km in diameter and surpass 460 to

610 m in height-largest shield volcano (and the largest active volcano) in

the world isMauna Loa in Hawaiʻi,• projects 4,169 m above sea level, and is over 97 km

wide.• contain 80,000 km3 of basalt

The Hawaiian shield volcanoes and the Galápagos islands are

unique.

-are not located near any plate boundaries; instead, the two

chains are fed by the movement of oceanic plates over hotspot

-their lavas are characterized by high levels ofsodium, potassium, and aluminum

Hallmarks of shield volcanism:

• rift zones - linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit.• lava tubes -natural conduits through which lava travels• multiple splatter (or cinder) cones• calderas

East Rift Zone on KilaueaThurston Lava Tube in

Hawaii Volcanoes National Park, Hawaii.

Valentine Cave in Lava Beds National Monument,

California. This shows the classic tube shape and the curbs on the wall mark

former flow levels.

Lava tube: hollow beneath a lava flow.

Lava Tubein Hawaii

Distribution

Image of the sites of active and dormant shield volcanoes around the world

Shield volcanoes are found worldwide.

They can form over:

• hotspots (Hawaiian-Emperor seamount chain and the

Galápagos Islands)

• over rift zones(Icelandic shields and the shield

volcanoes of the East Africa)

• found in ocean basins, although they can be found in

inland as well (East Africa)

Hawaiian islands

-the largest shield volcano chain in the world

Galápagos islands

-1,200 km east of Ecuador

Iceland

-major center of shield volcanic activity

Pahoehoe lava

flow in Hawaii.

Mars' shields

• 27 km in height and 563 km in diameter

• resemblance to the volcanoes of the Hawaiian Islands

• Olympus Mons- highest known mountain in

the solar system

Dangers -do not pose much threat to humans -they are hazardous to agriculture and infrastructure -1983 eruption of Kīlauea has destroyed over 200 structures and buried kilometers of highways

Extraterrestrial

Cinder conescoria cones, cinder and spatter cones

• they aren't famous• built from lava fragments called cinders• grow up in groups• often occur on the flanks of strato volcanoes and shield volcanoes • grow rapidly ( 250m in height and 500m in diameter)• have a bowl-shaped crater at the summit.

Most famous cinder cone-Paricutin(field in Mexico in 1943)

• lava flows covered 25 km²• cone -424 meters

• numerous in western North America cinders

Cinder cone (230 m high) in Lassen Volcanic National Park, CA.

Cerro Negro in Nicaragua (born in 1850)

• The Earth's most historically active cinder cone

• erupted more than 20 times

Schematic representation of the internal structure of a typical cinder cone Paricutin Volcano

Fissure vent• large flood basalts and lava channels• hard to recognize• crack in the ground• along rifts and rift zones (Iceland and the

Great Rift Valley in Africa) • often found in shield volcanoes

The Laki fissure system

-biggest eruption on earth in historical times-during the Eldgjá eruption A.D. 934, which releas

19.6 km³ of lava

Fissure vents of Hawaiian volcanoes-“curtains of fire”

Fissure eruption in IcelandA volcanic fissures and lava channels

Lava dome

High viscosity :1) high levels of silica in the magma2) degassing of fluid magma

Most of the preserved domes have high silica.

-heights -several hundred meters -grow slowly and steadily for months, years, or evencenturies

Image of the rhyolitic lava dome of Chaitén Volcano during its 2008–2009 eruption.

Hazards

pyroclastic flows, destruction of property, forest fires…

Characteristics

hemispherical dome shape

cycles of dome growth over long periods

sudden onsets of violent explosive activity

Steep-sided lava dome, Alaska

Subglacial volcano

• pillow shapes• pillow breccia (a rock composed of pillow fragments) and

hyaloclastite form

The shape -flattened top and steep sides.

• most common in Iceland and Antarctica• older formations -British Columbia and Yukon Territory,

Canada

• cause jökulhlaups (great floods of water)

the Grímsvötn Volcano beneath the Vatnajökull(Iceland)(November 1996) ice sheet erupted and

caused aJökulhlaup that affected more than 750 km² and

destroyedor severely damaged several bridges

Iceland’s Grimsvotn Volcano Is Erupting Remnants of bridge twisted by November 5, 1996 flood following Grímsvötn eruption

Stage 1. Early eruptions – pillow lavas and hyaloclastite

Stage 2b. Formation of a subglacial mound

Stage 3b. Formation of a tuya

type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet.

Mud volcanoGas-oil volcano

• associated with subduction zones

• 700 have been identified

• cooler temperature

• the largest mud volcano structures (10 kilometres in diameter and

700 metres in height)

• 86% methane, less carbon dioxide and nitrogen

• associated with petroleum deposits, tectonic subduction zones and

orogenic belts, lava volcanoes

• 1,100 mud volcanoes have been identified

Volcan El Totumo (Colombia)

15 m high and can accommodate 10 to 15 people on its crater

Volcan de Lodo El Totumo (Mud Volcano), Cartagena

Submarine volcano located near areas of tectonic plate movement,

known as ocean ridges exist in shallow water

There are three circumstances where tectonicplates can interact with each other and the Earth'smolten interior to form submarine volcanoes.

1. tectonic plate slides over a "hot spot" 2. where tectonic plates are spreading apart at the

mid-ocean ridges3. subduction

Pillowed Lava Flow

lava flow that formed

under water

interaction of water

with the molten lava

forms a thick glassy

crust around the

flowing lava

Scientists still have much to learn about the location and activity of underwater volcanoes.

The Kolumbo underwater volcano (Aegean Sea) was discovered in 1650 when it burst from the sea and erupted, killing 70 people on the nearby island of Santorini.

• seamounts• formed from extinct volcanoes, rising from a seafloor of 1,000

- 4,000 meters depth. • 30,000 seamounts occur across the globe, with only a few having been studied

Supervolcano

magma rises into the crust from a hotspot but is unable to break through the crust

pressure builds in a large and growing magma pool until the crust is unable to contain the pressure

form at convergent plate boundaries and continental hotspot locations

rate VEI 8 -"super eruptions“ colossal events that throw out at least

1,000 km3 Dense Rock Equivalent (DRE) of ejecta

rases virtually all life in a radius of hundreds of

kilometers from the site, and entire continental

regions further out can be buried meters deep in ash

Form circular calderas

remain for millions of years after all volcanic activity

at the site has died

every 50,000 years the Earth experiences a super-

volcano

1,000 sq km of land obliterated by pyroclastic ash

flows, the surrounding continent is coated in ash and

sulphur gases are injected into the atmosphere

Taupo in New Zealand,most recent super-volcano,

around 26,500 years ago

the most damaging super-volcano in human history

was Toba, on Sumatra, Indonesia, 74,000 years ago

-close to the equator

-temperatures were dramatically reduced

Volcano Types