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 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” emer- gency 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 (SiO 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 Materials extruded from a volcano  Pyroclastic materials – “fire fragments” Types of pyroclastic debrisTypes 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) Materials extruded from a volcano (continued)  Pyroclastic materials – “fire fragments” Types of pyroclastic debrisTypes 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 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 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 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 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 Intrusive igneous activity  Most magma is emplaced at depth in the Earth  Once cooled and solidified, it is called a pluton

Intrusive igneous activity 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 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 fine- grained 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  El Chichón, Mexico  Mount Pinatubo, Philippines