<<

1/31/2013

Can you predict the location of volcanoes?

What is causing this eruption? What factors influence its character?

“A is any from which , , or ashes, escape from underground or have done so in the past.”

There are three common types of : We learned from Chapter 5 that BASALTIC magma (and lava) Basaltic lava flows easily because of its can be , low (low gas content). The intermediate, or low viscosity is due to low silica content. Aa - rough, fragmented lava . How does ANDESITIC blocks called “clinker” magma chemistry influence the of volcanic RHYOLITIC eruptions?

Pahoehoe - smooth, shiny, and ropy surface

There are three common There are three common types of magma: types of magma: BASALTIC BASALTIC ANDESITIC ANDESITIC Andesitic magma erupts explosively because it tends to have high gas content. It is viscous and therefore traps gas, builds RHYOLITIC pressure and explosively erupts. High viscosity is related to high silica content Rhyolitic magma erupts catastrophically because Rhyolitic lava flow it has high gas content. It is viscous and therefore RHYOLITIC traps gas, builds pressure and explosively erupts. High viscosity is related to high silica content – an abundance of silica polymers (chains etc.) to the high viscosity. Mount St. Helens, 1980

1 1/31/2013

EXPLOSIVE Comparison of common magma types ERUPTIONS are fueled by violent releases of

Pyroclastic is produced by = airborne = gravity-driven down the slopes

A cataclysmic Plinian-style eruption (schematic drawing)

Reunion EFFUSIVE ERUPTIONS

RELATIVELY FLUID LAVA FLOW

DETERMINED BY: http://dsc.discovery.com/videos/ultimate-guide-to-volcanoes-pyroclastic-flow.html • viscosity (low) • temperature (high) • gas content of magma http://www.youtube.com/watch?v=yjL7UjogUaI (low)

2 1/31/2013

Volcanic products? Lava, gas, pyroclastic debris released from a volcano can be as deadly as the hot, fiery lava. Aā 1000 to 1100°C Pāhoehoe 1100 to 1200°C

Volcanoes can be classified into 6 major types TYPES OF PYROCLASTIC DEBRIS based on their size, shape, and origin

Large-scale Volcanic Terrains no central vent network of source material ASH generally massive

PUMICE VOLCANIC BOMBS

Central Vent Volcanoes central vent summit crater flank eruptions fissure eruptions

VOLCANIC BLOCK WELDED

COMPARISON OF SIX TYPES OF VOLCANOES SHIELD VOLCANOES ARE A TYPE OF CENTRAL VENT VOLCANO.

Mauna Loa

3 1/31/2013

Shield Volcano • Low silica, low gas magma originates in the . • Fluid, basaltic lava results in “Aa” and “Pahoehoe”. • Low viscosity creates broad, gentle slopes. • Sometimes, Phreatomagmatic eruptions (rapid expansion of ) occur when lava contacts .

Hawai‘i • Eight main are exposed tips of the Hawaiian . • Age range is modern to ~6 million years old. • Volcanoes develop on the as it moves across the Hawaiian .

Hawai‘i • Hawaiian volcanoes progress through pre-shield Lōʻihi, shield and Kīlauea, post-shield Mauna Kea, , and Haleakalā, erosional , Lāna‘i, and Wai‘anae, and rejuvenated Ko‘olau and West stages. Ni'ihau • As the islands age, they erode and subside, becoming and . Koolau Waianae Wailau Lōihi Mauna Loa West Maui Lāna‘i Haleakalā Kohala

Hualālai Mauna Kea

Mauna Loa Kīlauea Lōihi

4 1/31/2013

Diamond Head

Geologists have known for years that Maps of the seafloor indicate that massive have occurred pieces of the two shields that make have been missing

Koolau Shield

Our islands are carved by massive landslides

Waianae Shield

Measurements show the flank of Kilauea is moving 10 cm/yr to the SE

1975 Kalapana quake shifted the flank 8 m horizontal and 3 m vertical

Over 17different landslides have been identified

Koolau reconstructed

Will the south shore of the Big Island slide?...it already is!

5 1/31/2013

Volcanoes can be classified into 6 major types formation based on their size, shape, and origin

Large-scale Volcanic Terrains no central vent network of source material generally massive

Central Vent Volcanoes central vent summit crater flank eruptions fissure eruptions

Layered with lava Composite Volcano or Flows and ashfall Cinder Cones Deposits – massive • high lava fountains on the vents of shield volcanoes.

• composed of pyroclastic debris. • caused by high gas content.

Mount Mageik, Katmai National Park

FEATURES OF STRATOVOLCANOES Mt. Fuji (composite volcanoes)

• Alternating andesitic lava flows and layers of explosively ejected pyroclastics. • Magma is intermediate, making the lava viscous and difficult to erupt. • Explosive eruptions due to buildup of gases.

6 1/31/2013

•Steep slopes •Explosive •Irregular outline from past explosions • magma •Relatively high silica content

Lava Dome – a plug that prevents eruption

Pressure builds behind Mt. , the plug until it blows…

What happens when Sticky silica-rich the plug is blown? magma controls volcano shape, Plinian-style explosivity, and eruption…don’t stick behavior around to watch

Pyroclastic flows

Major atmospheric impacts Volcano is blasted to pieces

Lahar

Mt. Pinatubo - 1991

7 1/31/2013

FEATURES OF COMPLEXES

• High -silica, high-gas . • Massive explosions (most explosive of all types).

• Collapse, producing an Aniakchak Caldera “inverse volcano”, Rhyolite Caldera Complexes Are Central or Caldera (Spanish for cauldron). Vent Volcanoes.

Large -scale volcanic terrains lack a central vent

San Francisco Monogenetic Fields Poorly understood. Multiple vents and cinder cones. Erupt at different times. Grow laterally. Usually a single magma source Low magma supply

San Francisco Volcanic Field

8 1/31/2013

Large Igneous Province

Fed by massive mantle plumes Very fluid lava erupting rapidly and with great volume over thousands of years. basalts, , Caused by flood basalts (especially fluid basaltic ) Do LIP’s mark beginning of hotspots? Discharge over time through long fissures (cracks). Create large .

Columbia River Basalts

submarine Mid-ocean

develop at Spreading Centers Basaltic flow creates global network of interconnected ridges

Most volcanoes are associated with spreading center Spreading Center Volcanism volcanism, arc volcanism, or

Arc Volcanism Explosive rhyolitic, andesitic, and basaltic lavas, divergent plate margins, mid-ocean ridges Spreading Center Volcanism Fluid basaltic lavas, divergent plate margins, mid- ocean ridges

Intraplate Volcanism aka” midplate volcanism”, shield volcanoes, rhyolite caldera complexes, and monogenetic fields

9 1/31/2013

10