Volcanoes and Volcanic Hazards

Volcano

Naturally occurring landform produced when lava erupts to the surface.

Crater

Nearly circular / funnel-shaped depression produced by the ejection of rocks during volcanic eruptions.

Vent

Terminal point of a conduit/pipe. Leads to the crater.

Condit / Pipe

Localized pathway of magma.

Fissure vent

Long, linear fractures from which lava is erupted. Common in oceanic ridges, continental rifts, and hotspots.

Parasitic cone

Produced by flank eruptions.

Flank eruption

An eruption in which lava erupts out of a vent on the side of a volcano. Common in old volcanoes.

Caldera

A crater more than 1km in diameter. Produced by the collapse of the volcano summit due to magma loss at the chamber below.

Factors affecting explosivity of eruptions

Composition, temperature, amount of dissolved gasses

Factors affecting viscosity of magma

Temperature, silica content, amount of dissolved volatiles

Composition of magma

Melt, solid portion (rocks, minerals), volatiles (H2O, CO2 and SO2)

Active volcanoes (PHIVOLCS)

Erupted within the last 600 years (historical). Erupted within the last 10,000 years based on analysis of volcanic deposits.

Potentially active volcanoes (PHIVOLCS)

Morphologically young-looking but with no historical or analytical records of eruption.

Inactive volcanoes (PHIVOLCS)

No recorded eruptions. Intensely weathered and eroded. Have deep and long gullies.

Aa lava flow

Rough, jagged blocks. Sharp edges, spiny projections. More viscous than pahoehoe.

Pahoehoe lava flow

Less viscous than aa. Smooth, ropy surface.

Can an aa transform to pahoehoe?

No.

Can an pahoehoe transform to aa?

Yes. Happens when pahoehoe flow cools or enters a region of steep slope.

Block lava

Composed of andesitic and rhyolitic lava Upper surface consists of massive, detached blocks. Like aa. Slightly curved, smooth.

Pillow lava

Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows. Useful in geologic reconstructions.

Ash

Lapilli

2-64mm. Means "little stones"

Accretionary lapilli

Hailstone-like clumps of wet ash that fall from a volcanic eruptive cloud.

Volcanic block

Large pieces of pyroclastic material that is made up of rock.

64mm. Hardened lava.

Volcanic bomb

A projectile of hot magma or rock that is blown from the vent during a volcanic eruption. These solidify in flight and frequently form an elongated rock of streamlined shape. >64mm.

Pumice

From intermediate/felsic magma. Vesicular, less dense that scoria, light in color.

Scoria

From basaltic magma. Vesicular, more dense that pumice, dark in color.

Shield volcano

Broad, gentle-sloping (2-10 degrees). Formed from accumulations of basaltic lava. Common in hotspots.

5 volcanoes of Big Island, Hawaii

Mauna Loa, Mauna Kea, Kilauea, Kohala, and Hualalai

Lava fountain

Fiery basaltic lava ejections that reach several hundred feet high.

Spatter

Airborne blobs of liquid lava emitted by lava fountains.

Welded spatter

Spatter that solidifies at the base of the lava fountains. Also called agglutinate deposits.

Spatter cone

Form where welded spatter accumulates around a central vent. Typically <20m tall.

Spatter rampart

Linear ridges formed when lava is erupted along a fissure; can be found on both sides of the fissure.

Pele's hair

Thin glassy material formed when lava droplets are propelled through the air and stretched into golden, acicular strands (diameters of ~0.5mm and lengths up to 2m).

Pele's tears

Black, glassy, streamlined particles.

Lava tube

Shallow subterranean tunnels channeling lava beneath the thin, solidified basaltic roofs. 1m-tens of km long.

Lava levee

Feature of lava tubes. Elevated lateral banks that contain the lava flow within a stream-like channel.

Lavacicle

Feature of lava tubes. Lava stalactites hanging from the ceiling, lava drips and flow lines occurring on the walls.

Pyroclastic cone

Steep-sided (30-35 degrees). Made from tephra. Sometimes extrude lava at the base of cone. Have deep and large craters. Produced by short-lived eruptions.

Scoria cone

Composed predominantly of basaltic material.

Cinder cone

Consisting of ash, lapilli, and bomb-sized particles of various compositions that accumulate as circular to oval-shaped conical volcanoes.

Composite volcano / Stratovolcano

A large, steep-sided volcano that results from explosive eruptions of andesitic and rhyolitic lavas along convergent plate boundaries. Nearly symmetrical. Capable of explosive eruptions.

Volcanic spine

Hypabyssal. Formed when viscous magma crystallizes within the composite volcano and pushed out of vent (recall Pelée, 1902).

Volcanic plug

Consists of magma that solidifies within the throat or conduit of a volcano. Prevents the release of lava.

Volcanic dome

Steep-sided, blister-like forms that occur within volcanic craters. Inflated areas generated by the accumulation of viscous, often glassy, blocky dacitic, rhyolitic, or trachyandesitic composition, on the surface or in shallow subsurface (recall Saint Helens, 1980).

Nuee ardente

Incandescent, hot (1000 deg. Celsius) volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion. Can move at speeds of 200kph. Caused by collapse of lava dome. Produced block and ash deposits.

Block and ash flow

Produced from the collapse of a lava dome that subsequently produced a nuee ardente. Deposits are mixture of volcanic blocks and ash.

Pyroclastic surge

A type of pyroclastic flow having higher steam content and less pyroclastic material. Surges are lower density, more dilute, high velocity, and may flow outward in a radial pattern. Generated by column collapse or directed blasts.

Pumice flow

Low to moderate density, hot vesiculated flows. Due to silicic nature of magma. Produced from collapse of vertical plumes. Forms ignimbrites.

Ignimbrite

Light-colored deposit produced by pumice flows. Contain features like columnar jointing indicating slow cooling.

Scoria flow

Low to moderate density, hot vesiculated flows. Due to andesitic-basaltic nature of magma. Produced from collapse of vertical ash plumes.

Lahar

Volcanic mudflows up to tens of meters thick with the consistency of wet cement. Dense mud slurries of ash- to bomb-sized particles that are easily remobilized in the presence of water. Can move at speeds of 100kph.

When can lahar form?

1. During volcanism and active pyroclastic flows (Nevado del Ruiz, 1985)
2. Immediately after volcanism when deposits are easily remobilized Saint Helens, 1980).
3. Long after volcanism. Even on dormant/inactive volcanoes when deposits are remobilized (Pinatubo, Mayon).

Volcanic neck

A deposit of hardened magma in a volcano's pipe. Exposed when outer volcano body erodes.

Diatreme

A type of pipe exceeding 200km in depth. Transports unaltered magma. Source of kimberlites.

3 types of caldera

Crater lake-type, Hawaiian-type, and Yellowstone-type

Crater lake-type caldera

Form from the collapse of the summit of a large composite volcano following an eruption that partially emptied the magma chamber. Eventually fill with rainwater/groundwater.

Hawaiian-type caldera

Form gradually from the collapse of the summit of a shield volcano following the subterranean drainage of the central magma chamber.

Yellowstone-type caldera

Form from the collapse of a large area after the discharge of large volumes of silica-rich pumice and ash. Tend to exhibit a complex history. Very large.

Tuff ring

Gently sloping, circular structures composed of stratified glassy volcanic debris and scoria. Develop due to the explosive eruption of basalt in a lake, beach, or wetland environment. Shallow water cinder cones in which pyroclastic material has been reworked by wave action, distributing volcanic debris around the vent.

Tuff cone

Circular volcanic cones formed by the eruption of basalt in water. Smaller and steeper that tuff rings. Small due to less explosive eruptions and less eruption duration.

Maar

Low relief volcanic centers that form by shallow explosive phreatomagmatic eruptions. Volcanic crater fills with water to form a freshwater or saline lake.

Phreatomagmatic eruption

Steam-driven eruptions produced when magma or lava heats groundwater, converting it to steam. Results to violent explosions in which steam, hot water, and/or pyroclastic debris are hurled into the air.

Phreatic eruption

Eruption of heated water and steam without magma. Due to percolation of groundwater downward toward a high temperature magma reservoir. Produces siliceous sinters, tufa, sulfides, and other minerals associated with hydrothermal activity.

Hot spring

Contains groundwater heated by close proximity to magma. Develop in areas of unusually high geothermal gradients.

Geyser

Eruptive hot springs that eject fountains of heated water periodically. Erupts as groundwater heated above 100°C; because boiling point of water is higher under pressure, superheated water rises, converts to steam, and is ejected explosively. Develop in areas of unusually high geothermal gradients.

Fumarole

Emit mixtures of steam and other gases such as H2S. Gas sublimation produces sulfur deposits. Develop in areas of unusually high geothermal gradients.

Jokulhlaups

Release of glacial meltwater due to sub-glacial volcanic activity. They are sudden flood burst of glacial water in lakes or water contained within the glacier.

Quiet eruption

From low viscosity lava. Non-explosive (occasionally explosive) . Produces lava flows, lava fountains, and lava lakes.

Explosive eruption

Occur at convergent margins and rhyolite caldera complexes. Characterized by massive ash clouds >10km in height, glowing nuees ardentes, and devastating pyroclastic flow and lahars. Consist of a series of short, violent bursts generated by the shattering of solid plugs of andesitic-rhyolitic composition (throat-clearing phase).

Types of quiet eruptions

Hawaiian Icelandic Strombolian Surtseyan

Types of explosive eruptions

Vulcanian Vesuvian Peléean Plinian Ultraplinian

Hawaiian eruption

Eruptions begin as fissures, evolving to central vent flows and the generation of large shield volcanoes, fiery basaltic lava fountain eruptions, quiet lava flows, and cinder cones.

Icelandic eruption

Persistent fissure eruption of low viscosity basaltic lava flows. Prolonged quiet eruptions may generate lava plateaus and flood basalts.

Surtseyan eruption

Phreatomagmatic. Explosive, steam-blast eruptions with lava flows and pyroclastic debris. After Surtsey's 1963 eruption.

Strombolian eruption

Periodic bursts of moderately explosive eruptions (<5km high) with great concentrations of pyroclastic fragments and incandescent basaltic lava flows.

Vulcanian eruption

Explosive eruptions of basaltic to rhyolitic viscous lava and large volumes of volcanic ash plumes (<25km high) and pyroclastic debris.

Vesuvian eruption

Violent eruptions of volcanic debris ejected, scattering ash over thousands of square kilometers.

Peléean eruption

Occur when viscous magma, typically andesitic to rhyolitic, erupts. Characterized by presence of glowing avalanche of volcanic ash, formation of lava domes, and short flows of ash or creation of pumice cones.

Plinian eruption

Tephra eruptions emit immense clouds of ash >11km in height into the stratosphere.

Ultraplinian eruption

Violent tephra eruptions of volumes >1km3 and ash cloud heights of 25-55km.

Volcanism at convergent plate margins

Results from dehydration of oceanic crust and the overlying wedge of mantle. Commonly andesitic. Parallel to trench. Volcanoes ~300km from trench.

Volcanism at divergent plate margins

Produces 60% of global lava. Due to decompression melting. Produces basaltic lava. Common features are pillow lavas and seamounts.

intraplate volcanism

Within plate. Due to mantle plume. Melting due to decompression. Produces hot spots.

Mantle plume

100-150 degrees Celsius hotter than normal mantle material. Begin from core-mantle boundary (ULVZ). Have bulbous head and thin stem.

Hot spot

Surface manifestation of mantle plumes. Forms linear chains as plate moves. There are ~40 worldwide.

What are the parts of a vertical plume / eruption column?

Gas thrust region Convective thrust region Umbrella region

Gas thrust region

Lower region. Material thrusted from the vent move through expanding gases at velocities ranging from 100-600 m/s.

Convective thrust region

Upper region. Produced by the convective rise of heated atmospheric gases and fragments.

Umbrella region

Similar to the mushroom-shaped heat cloud produced by thermonuclear bomb explosions. Begins to spread laterally as the result of temperature inversions in the atmosphere.

Rhyolite caldera complex

Large volcanic features that lack the typical, highly elevated landform associated with most volcanoes. Eruption so violent that the whole volcanic structure collapsed to form a large caldera.

Volcanic hazards

Associated with eruption and/or post-eruption events.

Types of volcanic hazards

Pyroclastic flow/surge Lava flows Volcanic gas Volcanic ash Volcanic earthquakes Landslides Volcanic tsunami Lahar

How to monitor volcanoes?

Tilt meters, laser ranging devices to detect movement of the ground, local magnetic field, water levels and water temperature, more gas, more earthquakes in an area.

Supervolcano

Large volcanic features that lack the typical, highly elevated landform associated with most volcanoes. Eruption so violent that the whole volcanic structure collapsed to form a large caldera.

Inverse volcano

Large volcanic features that lack the typical, highly elevated landform associated with most volcanoes. Eruption so violent that the whole volcanic structure collapsed to form a large caldera