Chapter 5 Flashcards
Volcanic Eruptions
Lava flows
molten rock that flows across the ground
Pyroclastic debris
solid fragments ejected during eruptions (ash, pumice, volcanic bombs)
Volcanic gases
gases such as water vapor, CO₂, and sulfur compounds released from magma.
pyroclastic flow
fast-moving avalanche of hot ash, gas, and volcanic material
lahar
a volcanic mudflow composed of water and volcanic ash/debris that moves down volcanic slopes, often triggered by heavy rain or melting snow.
Shield volcanoes
have broad, gentle slopes from low-viscosity basaltic lava flows
Stratovolcanoes
are steep and layered due to alternating lava flows and pyroclastic eruptions, often from more viscous andesitic or rhyolitic lava.
Cinder cones
small, steep hills of pyroclastic fragments, formed from gas-rich basaltic lava that erupts explosively.
Why do some volcanic eruptions consist mostly of lava flows, while others are explosive and do not produce flows?
Eruptions depend on magma viscosity and gas content. Low-viscosity, gas-poor basaltic magma results in gentle lava flows, while high-viscosity, gas-rich magma traps gas and pressure, leading to explosive eruptions with pyroclastic material.
What processes may lead to hot-spot eruptions?
Hot-spot eruptions are caused by mantle plumes, which are columns of hot material rising from deep within the mantle. These plumes create melting in the lithosphere as they reach shallow depths, leading to volcanic activity independent of tectonic boundaries.
How do continental-rift eruptions form flood basalts?
In continental rift settings, decompression melting of the mantle produces large volumes of basaltic magma. This magma can erupt through fissures, spreading out as vast, flat lava flows, forming extensive flood basalts.
island arc
a chain of volcanic islands formed above a subducting oceanic plate at an ocean-ocean convergent boundary
continental arc
forms along the edge of a continent above a subducting oceanic plate at an ocean-continent convergent boundary.
Identify some of the major volcanic hazards, and explain how they develop.
Lava flows can destroy property; pyroclastic flows and ash falls pose severe hazards to life, air quality, and buildings; lahars can bury settlements; volcanic gases can cause respiratory problems; volcanic tsunamis may occur if an eruption disturbs bodies of water.
How do geologists predict volcanic eruptions?
Geologists monitor earthquakes, gas emissions, ground deformation, and temperature changes around a volcano. Increased seismic activity or gas release often precedes eruptions, helping predict potential activity.
Explain how steps can be taken to protect people from the effects of eruptions.
Evacuation plans, hazard mapping, early warning systems, and exclusion zones around volcanoes can minimize risk. Public education and communication also ensure people know evacuation procedures and danger areas.
Accretionary Lapilli
Small, spherical pellets of volcanic ash that form when wet ash particles clump together as they fall during an eruption.
Active Volcano
A volcano that is currently erupting, showing signs of erupting soon, or has erupted in recent history.
Ash
Fine-grained volcanic material, smaller than 2 mm, expelled during explosive eruptions that can travel great distances.
Block
Large, angular fragments of solid rock ejected during a volcanic eruption, often originating from the volcano’s vent or walls.
Blocky Lava
Lava with a rough, jagged surface, formed when highly viscous lava cools and breaks into angular blocks as it flows.
Bomb
Large, rounded fragments of lava ejected during an explosive eruption, which cool in flight and take on aerodynamic shapes.
Caldera
A large, depression formed when a volcano’s summit collapses following an explosive eruption that empties the underlying magma chamber
Cinder Cone
A small, steep-sided volcanic cone made up of pyroclastic fragments such as cinders, formed by gas-rich, basaltic lava eruptions.
Columnar Jointing
A pattern of fractures that form during the cooling and contraction of lava, resulting in hexagonal columns.
Crater
A circular depression at the summit of a volcano, formed around the central vent by explosive eruptions or collapse.
Dormant Volcano
A volcano that hasn’t erupted in a long time but could become active again in the future.
Effusive Eruption
A type of eruption where low-viscosity lava flows steadily from a vent, resulting in gentle lava flows rather than explosions.
Eruptive Style
The characteristic behavior of a volcano’s eruption, influenced by magma composition, gas content, and eruptive dynamics (e.g., explosive or effusive).
Extinct Volcano
A volcano that geologists consider unlikely to erupt again, often due to its isolation from a magma source.
Fissure
A linear crack or fracture in the ground through which lava erupts, often leading to extensive lava flows.
Flood Basalt
Vast lava flows that cover large areas, produced by high-volume eruptions from fissures, often associated with large igneous provinces.
Ignimbrite
A rock formed from the deposition of pyroclastic flows, typically composed of compacted ash, pumice, and volcanic fragments.
Lahar
A volcanic mudflow composed of water and volcanic ash/debris that flows down the slopes of a volcano, often triggered by rainfall or melting ice.
Lapilli
Small fragments of pyroclastic debris, between 2 mm and 64 mm, that are ejected during an eruption.
Large Igneous Province (LIP)
A region with extensive igneous rock deposits, often created by massive volcanic eruptions over a relatively short geological timeframe.
Lava Tube
A tunnel-like passage within a lava flow, formed as the surface of the flow cools and solidifies while molten lava continues to flow beneath.
Magma Chamber
A subterranean reservoir of molten rock beneath a volcano, which supplies magma for eruptions.
Pahoehoe
A type of basaltic lava flow with a smooth, ropy surface, formed by the movement of very fluid lava.
Pumice Lapilli
Small, light, frothy volcanic fragments formed from gas-rich magma that cools rapidly, often found in pyroclastic deposits.
Pyroclastic Debris
Fragments of volcanic rock, ash, and pumice produced by explosive volcanic eruptions.
Pyroclastic Flow
A fast-moving avalanche of hot gas, ash, and volcanic fragments that moves rapidly down a volcano during explosive eruptions.
Scoria Cone
Another term for a cinder cone; a small, steep-sided volcano built primarily of pyroclastic fragments from gas-rich basaltic magma.
Shield Volcano
A broad, gently sloping volcano formed by low-viscosity basaltic lava flows, creating a shield-like profile.
Stratovolcano
A large, steep-sided volcano built by alternating layers of lava flows, ash, and pyroclastic material, often associated with explosive eruptions.
Tephra
General term for any type of volcanic material ejected during an eruption, including ash, lapilli, and volcanic bombs.
Tuff
Rock formed from compacted volcanic ash and other pyroclastic materials, often found in layers from past eruptions.
Vesicle
A small cavity within volcanic rock that was formed by trapped gas bubbles during solidification.
Volcanic Debris Flow
A dense mixture of water, volcanic rock, and mud that moves downslope from a volcano, usually triggered by heavy rain or melting snow.
Volcaniclastic Deposit
Any deposit of volcanic material, including ash, lapilli, and pyroclastic rock fragments, which can be produced by eruptions or volcanic weathering.
Volcano
A geological structure formed when magma from within the Earth reaches the surface, leading to eruptions of lava, ash, and gases.
Effusive Eruptions
lava pours out of a vent or fissure
Explosive Eruptions
Volcanic products are erupted into the air due to the gas in the magma
Tectonic Setting of Stratovolcanoes
Subduction zones: high water content with more felsic magmas
Phreatomagmatic Eruptions
the lava lake begins to drain out the center of a crater, drops below water, steam pressure builds and volcano erupts
Flood Basalts
eruptions of massive volumes of basaltic magma and has been attributed to the arrival of a new plume
Volcanic Hazards
gravity driven lateral flow of gas, pumice, and ash
