UNDERSTANDING VOLCANOS Dr Walter Hays Global Alliance For

UNDERSTANDING VOLCANOS Dr. Walter Hays, Global Alliance For Disaster Reduction

ESSENTIAL KNOWLEDGE FOR SOCIETAL SUSTAINABILITY A FRAMEWORK FOR UNDERSTANDING THE IMPACTS OF VOLCANIC ERUPTIONS ON PEOPLE AND THEIR COMMUNITIES

GLOBAL DISTRIBUTION OF 1, 500 ACTIVE VOLCANOES

ERUPTIONS OF MOUNT MERAPI May 15, and June 6 - 8, 2006

LOCATION IN CENTRAL JAVA

MOUNT MERAPI RECEIVED CLOSE ATTENTION ON APRIL 18

INDONESIA’S MOUNT MERAPI ERUPTED ON MAY 15, 2006 § Mount Merapi, a stratovolcano, emitted lava, debris, and a pyroclastic flow (or cloud) on May 15.

MAY 15, 2006 ERUPTION § Hot ash released.

MAY 15, 2006 ERUPTION § Volcanic ash turned everything white

MAY 15, 2006 ERUPTION § School children wore masks to counter adverse health effects of breathing volcanic ash.

MAY 15, 2006 ERUPTION § Volcanic ash covered crops and vegetation.

MAY 15, 2006 ERUPTION § Volcanic ash covered automobiles and affected jet airline traffic.

MOUNT MERAPI ERUPTED AGAIN ON JUNE 6 -8, 2006 § Mount Merapi volcano emitted lava, debris, and pyroclastic flows (superheated clouds of gas) on Tuesday, June 6 and Wednesday, June 7.

EXPLOSIVENESS OF JUNE 8 ERUPTION SENT 15, 000 FLEEING

EVACUATION § 11, 000 from three districts evacuated to schools and otheren “safe haven” emergency shelters.

MANY CHOSE TO EVACUATE § Many citizens chose to evacuate. § Evacuation was ordered. § Villagers remembered the 1994 disaster.

MANY CHOOSE NOT TO EVACUATE § Many citizens chose not to evacuate because shelters are boring and they wanted to provide for livestock and tend crops.

ESSENTIAL KNOWLEDGE ON VOLCANOES

Plate tectonics and volcanic activity § Global distribution of volcanoes §Most volcanoes are located within or near ocean basins §Basaltic rocks: in oceanic and continental settings §Granitic rocks: in continental settings

The nature of volcanic eruptions § Three physical characteristics of a magma control its viscosity, the physical property that ultimately determines the “violence” or explosiveness, of the eruption: § Composition § Temperature § Dissolved gases

The magma affects the severity of a volcanic eruptions §In summary –Basaltic Magmas = mild eruptions –Rhyolitic or Andesitic Magmas = explosive eruptions

The nature of volcanic eruptions § Viscosity is a measure of a material’s resistance to flow § Factors affecting viscosity §Temperature - Hotter magmas are less viscous §Composition - Silica (Si. O 2) content

The nature of volcanic eruptions –Higher silica content = higher viscosity (e. g. , felsic lava such as rhyolite) –Lower silica content = lower viscosity (e. g. , mafic lava such as basalt)

The nature of volcanic eruptions §Dissolved gases –Gas content affects magma mobility –Gases expand within a magma as it nears the Earth’s surface due to decreasing pressure –The violence of an eruption is related to how easily gases escape from magma

Materials extruded from a volcano § Lava flows § Basaltic lavas exhibit fluid behavior § Types of basaltic flows – Pahoehoe lava (resembles a twisted or ropey texture) – Aa lava (rough, jagged blocky texture) § Dissolved gases § 1% - 6% by weight § Mainly H 2 O and CO 2

Materials extruded from a volcano § Pyroclastic materials – “fire fragments” • Types of pyroclastic debris –Ash and dust - fine, glassy fragments –Pumice - porous rock from “frothy” lava –Cinders - pea-sized material

Materials extruded from a volcano (continued) § Pyroclastic materials – “fire fragments” • Types of pyroclastic debris –Lapilli - walnut-sized material –Particles larger than lapilli § Blocks - hardened or cooled lava § Bombs - ejected as hot lava

Volcanoes § General features § Opening at the summit of a volcano – Crater - summit depression < 1 km diameter – Caldera - summit depression > 1 km diameter produced by collapse following a massive eruption § Vent – surface opening connected to the magma chamber § Fumarole – emit only gases and smoke

Volcanoes § Types of volcanoes §Shield volcano –Broad, slightly domed-shaped –Generally cover large areas –Produced by mild eruptions of large volumes of basaltic lava –Example: Mauna Loa on Hawaii

Volcanoes §Cinder cone –Built from ejected lava (mainly cinder-sized) fragments –Steep slope angle –Small size –Frequently occur in groups

Volcanoes §Composite cone (stratovolcano) –Most are located adjacent to the Pacific Ocean (e. g. , Fujiyama, Mt. St. Helens) –Large, classic-shaped volcano (1000’s of ft. high and several miles wide at base)

Mt. St. Helens – prior to the 1980 eruption

Mt. St. Helens (after the 1980 eruption)

Volcanoes §Composite cone (stratovolcano) continued –Composed of interbedded lava flows and pyroclastic debris –Most violent type of activity (e. g. , Mt. Vesuvius)

Volcanic Hazards §Nuée ardente – §A Fiery pyroclastic flow made of hot gases infused with ash and other debris §Also known as “glowing avalanches” §Move down the slopes of a volcano with velocities approaching 200 km/hour

Volcanic Hazards §Lahar – volcanic landslide or mudflow §Mixture of volcanic debris and water §Move down slopes of volcano and stream valleys with velocities of 30 to 60 miles/hour

volcanic hazards § Pyroclastic flow §Felsic and intermediate magmas §Consists of ash, pumice, and other debris §Material ejected at high velocities §Example: Yellowstone plateau

Other volcanic landforms § Caldera §Steep-walled depressions at the summit §Generally > 1 km in diameter §Produced by collapse §Example: Crater Lake, Oregon

Other volcanic landforms § Fissure eruptions and lava plateaus § Fluid basaltic lava extruded from crustal fractures called fissures § Example: Columbia River Plateau § Lava domes § Bulbous mass of congealed lava § Associated with explosive eruptions of gas-rich magma

Other volcanic landforms § Volcanic pipes and necks §Pipes - short conduits that connect a magma chamber to the surface §Volcanic necks (e. g. , Ship Rock, New Mexico) - resistant vents left standing after erosion has removed the volcanic cone

Shiprock, New Mexico

Intrusive igneous activity § Most magma is emplaced at depth in the Earth §Once cooled and solidified, it is called a pluton

Intrusive igneous activity § Nature of plutons §Shape - tabular (sheetlike) vs. massive §Orientation with respect to the host (surrounding) rock –Concordant vs. discordant

Intrusive igneous activity § Types of intrusive igneous features §Dike – a tabular, discordant pluton §Sill – a tabular, concordant pluton (e. g. , Palisades Sill in New York)

Intrusive igneous activity § Types of intrusive igneous features §Lacolith –Similar to a sill –Lens or mushroom-shaped mass –Arches overlying strata upward

Intrusive igneous activity § Intrusive igneous features continued §Batholith –Largest intrusive body –Surface exposure > 100+ km 2 (smaller bodies are termed stocks) –Frequently form the cores of mountains

Plate tectonics and igneous activity § Global distribution of igneous activity §Most volcanoes are located within or near ocean basins §Basaltic rocks: oceanic and continental settings §Granitic rocks: continental settings

Plate tectonics and igneous activity § Igneous activity at plate margins §Spreading centers –Greatest volume of volcanic rock is produced along the oceanic ridge system

Plate tectonics and igneous activity § Igneous activity at plate margins § Mechanics of spreading § Decompression melting of the mantle occurs as the lithosphere is pulled apart § Large quantities of basaltic magma are produced

Plate tectonics and igneous activity § Subduction zones –Occur in conjunction with deep oceanic trenches –Location of partial melting of descending plate and upper mantle –Rising magma can form either § An island arc if in the ocean § A volcanic arc if on a continental margin

Plate tectonics and igneous activity §Subduction zones are associated with the Pacific Ocean Basin §The region representing the Pacific Rim is known as the “Ring of Fire” §Location of majority of world’s explosive volcanoes

Plate tectonics and igneous activity § Intraplate volcanism § Occurs within a tectonic plate § Associated with mantle plumes § Localized volcanic regions in the overriding plate are called a hot spot – Produces basaltic magma sources in oceanic crust (e. g. , Hawaii and Iceland) – Produces granitic magma sources in continental crust (e. g. , Yellowstone Park)

Volcanoes and climate § The basic premise §Explosive eruptions emit huge quantities of gases and finegrained debris §A portion of the incoming solar radiation is reflected and filtered out

Volcanoes and climate § Past examples of volcanism affecting climate §Mount Tambora, Indonesia – 1815 §Krakatau, Indonesia – 1883

Volcanoes Can Impact Regional And Global Climate § Modern examples §Mount St. Helens, Washington 1980 §El Chichón, Mexico - 1982 §Mount Pinatubo, Philippines - 1991