Volcanic Landforms

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.

Conduit / 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

Adventive/secondary 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 tall and 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.

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.

Central, fissure, and areal

3 main types of volcanic eruptions

Central eruption

Those that issue from a central pipe or vent; may erupt many numerous parasitic centers along a fissure on its flanks.

Fissure eruption

Those that issue from cracks or fissures but sometimes, they later erupt at separate centers.

Areal eruption

Polyrorofice volcanism. Scattered over wide areas; absence of eruption centers to occur at definite points for any length of time. Have individual volcanic structures that are small.

Aa lava flow

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

Pahoehoe lava flow

Less viscous than aa. Smooth, ropy surface.

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.

Monogenetic and polygenetic

Types of eruptive events.

Monogenetic

Where there is a single, usually small, eruption; usually associated with fissure volcano belts like fracture belts where openings appear once, then freeze over and reappear in another spot.

Polygenetic

Where there is a sequence of eruptive events, often with a cyclic variation in lava types. Usually associated with central volcanoes.

Shield volcano

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

Lava dome

Smaller-scale volcano that erupts liquid lava may produce a convex dome rather than a shield.

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.

Lava mound

Gently sloping mound, no sign of crater. Although they never had very pronounced craters but had lava welling right to the brim before solidification.

Lava disc

Made of basalt. Display jointing that is perpendicular to the lava skin on the upper surface and sides.

Cumulo-dome

Formed by acidic lava. Formed when viscous lava is extruded. Sags and spreads into convex dome-like bodies.

Mamelon

Domes built up by the eruption of successive flows of trachytic material. Have no crater.

Tholoid

Cumulo-dome/mamelon occurring within the crater of a large volcano. No crater.

Piton

Plug dome or upheaved plug. Formed from viscous magma that is extruded. Very rigid; looks like a monolith poking from the ground.

Coulees

Dome-lava-flow hybrids. They form where thick extrusions ooze on to steep slopes and flow downhill.

Peleean dome

A lava dome that grew in the vent of the volcano after the catastrophic eruption. Craggy with lava spines on the top and a talus deposit around the sides.

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.

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.

Scoria mound

A scoria cone that has no crater.

Littoral cone

Formed when lava reaches the sea and explodes to form a pile of ejecta. Hills built on both side of the lava stream entering the sea.

Maar

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

Nested scoria cone

Scoria cones produced at the center of large craters during the last phase of an eruption.

Fosse

The V-sectioned trough between the inner cone of a nested scoria cone and the crater wall.

Volcanic field

A place on Earth's surface where there are clusters of volcanic activity, including anywhere from 10 to 100 volcanoes.

Cryptovolcano

Roughly circular holes, sometimes with highly disturbed strata, where a volcanic origin is postulated, but where no igneous rock can be found. Formed by eruption of gas.

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.

Volcanic spine

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

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.

Volcanic neck

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

Diatreme

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

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.

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.

Jokulhlaup

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.

Hot spot

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

Resurgent caldera

A large topographic depression formed by piston-like collapse of overlying roof into magma chamber with a later central uplift of the caldera floor.

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.

Hot lahar

Rainwater mixed with hot eruption products, which are considered a primary hazard.

Cold lahar

Rainwater mixed unconsolidated ashes and nuees ardentes deposits. Considered a secondary hazard but also dangerous.

Banjir

Indonesian term for volcanic floods and the water drains in a short period