GEOL 1010 Exam 3 Study Guide: Volcanoes, Metamorphic Rocks, and Geologic Structures

Comprehensive vocabulary flashcards covering volcanic processes, sedimentary structures, metamorphic grades and environments, and geologic structures for GEOL 1010 Exam 3.

Viscosity

The resistance of magma or lava to flow.

Basaltic (Mafic) Lava

A type of lava characterized by low silica content and low viscosity.

Andesitic (Intermediate) Lava

A type of lava characterized by medium silica content and medium viscosity.

Rhyolitic (Felsic) Lava

A type of lava characterized by high silica content and high viscosity.

Effusive (Quiet) Eruptions

Volcanic eruptions characterized by runny lava with low silica and low viscosity that flows easily, forming shield volcanoes and large lava flows.

Explosive Eruptions

Violent volcanic eruptions driven by thick, high-silica, high-viscosity magma that traps gases until pressure builds and releases ash, pyroclastic material, and pyroclastic flows.

Volcanic Ash

Tiny rock and glass fragments measuring less than $2\,\text{mm}$.

Pyroclastic Material

Any rock material blasted from a volcano, including ash, lapilli, volcanic bombs, and blocks.

Pahoehoe

A hot, fast-moving, low-viscosity basaltic lava that cools with a smooth, ropy, wrinkled surface.

Aa

A cooler, slower-moving basaltic lava that is more viscous than pahoehoe and hardens into rough, jagged, sharp blocks.

Pillow Lava

Basaltic lava erupted underwater that solidifies into rounded, pillow-shaped blobs on the ocean floor.

Block Lava

Very viscous, slow-moving andesitic or rhyolitic lava that breaks into large angular blocks.

Conduit

The pipe through which magma rises from the magma chamber toward the surface.

Vent

The surface opening where lava and volcanic materials erupt.

Crater

A bowl-shaped depression located at the summit of a volcano.

Caldera

A large circular depression formed when a massive volcanic eruption empties the underlying magma chamber, causing the roof to collapse.

Shield Volcano

A broad volcano with gentle slopes built by repeated flows of basaltic lava during quiet eruptions (e.g., Mauna Loa and Kilauea).

Cinder Cone Volcano

A small, steep-sided volcano formed entirely from the accumulation of ejected pyroclastic fragments, volcanic ash, and cinders.

Composite Volcano (Stratovolcano)

A large, steep-sided volcano formed by alternating layers of lava and ash from alternating explosive and effusive eruptions (e.g., Mount Fuji and Mount St. Helens).

Fissure

A long crack in Earth's surface through which lava erupts.

Basalt Plateau

A large, flat region formed by repeated, extensive lava flows emerging from fissure eruptions (e.g., Columbia River Plateau).

Pyroclastic Flow

A fast-moving, deadly cloud of hot gases, ash, and rock fragments reaching temperatures over $800\,^\circ\text{C}$ and speeds exceeding $100\,\text{mph}$.

Lahar

A rapidly flowing volcanic mudflow consisting of a mixture of water, ash, and debris.

Hot Spots

Columns of hot mantle that rise through the lithosphere, producing volcanism away from plate boundaries (e.g., Hawaii and Yellowstone).

Sedimentary Structures

Features formed during sediment deposition that assist geologists in reconstructing past environments, water direction, and climate.

Bed

A single, distinct layer of sedimentary rock.

Bedding Plane

The boundary surface that separates individual sedimentary beds.

Mud Cracks

Sedimentary structures that form when wet mud dries and shrinks, indicating alternating wet and dry environmental conditions.

Metamorphic Rock

A rock altered from a pre-existing rock by heat, pressure, and chemically active fluids without melting.

Protolith

The original parent rock prior to undergoing metamorphism.

Metamorphism

The process that alters the mineral composition and texture of a rock due to heat, pressure, and chemically active fluids.

Metamorphic Grade

The degree of metamorphism a rock has undergone, categorized into low grade (little change), medium grade (moderate change), and high grade (major change).

Confining Pressure

Equal pressure applied to rock from all directions that compresses the rock without altering its shape.

Differential Stress

Stress that is applied unequally in different directions, causing rock deformation.

Foliated Texture

A metamorphic texture in which mineral grains are arranged in parallel layers or bands as a result of directed pressure.

Nonfoliated Texture

A metamorphic texture characterized by randomly arranged mineral grains lacking visible layering or bands (e.g., marble).

Slaty Cleavage

A low-grade metamorphic foliation texture characterized by very fine, thin planar layers.

Phyllitic Texture

A low-to-medium-grade metamorphic foliation texture featuring a wavy appearance and a silky sheen.

Schistosity

A medium-to-high-grade metamorphic foliation texture defined by visible, platy mica minerals.

Gneissic Banding

A high-grade metamorphic foliation texture defined by alternating bands of light and dark minerals.

Slate

The lowest-grade foliated metamorphic rock, characterized by slaty cleavage and formed from the protolith shale.

Phyllite

A low-to-medium-grade foliated metamorphic rock characterized by a phyllitic texture and a shiny surface.

Schist

A medium-to-high-grade foliated metamorphic rock displaying schistosity with visible flakes of mica.

Gneiss

The highest-grade foliated metamorphic rock, characterized by distinct alternating light and dark mineral bands.

Marble

A nonfoliated metamorphic rock derived from limestone, composed primarily of calcite, which reacts with acid.

Contact (Thermal) Metamorphism

Metamorphism driven primarily by high temperatures and low pressure occurring adjacent to magma intrusions.

Regional Metamorphism

The most common type of metamorphism, driven by both heat and high pressure across large areas during mountain-building events.

Hydrothermal Metamorphism

Metamorphism driven by the circulation of hot, chemically active fluids through rock, commonly occurring near mid-ocean ridges.

Burial Metamorphism

Metamorphism resulting from deep burial under thick sedimentary accumulations, which increases confining pressure and temperature.

Shock Metamorphism

Metamorphism caused by the intense pressure and high temperatures generated by meteorite impacts.

Subduction Zone Metamorphism

Metamorphism occurring where tectonic plates converge, characterized by high pressures and relatively low temperatures.

Deformation

Any change in the shape, position, or size of a rock body.

Elastic Deformation

A temporary form of deformation in which rock bends under stress but returns to its original shape once the stress is removed.

Ductile Deformation

A permanent form of deformation in which rock bends without fracturing, producing folds.

Brittle Deformation

Deformation in which rock fractures and breaks under applied stress, producing faults.

Compressional Stress

Differential stress that pushes rock masses together, producing folds and reverse faults.

Tensional Stress

Differential stress that pulls rock masses apart, producing normal faults.

Shear Stress

Differential stress that causes rock bodies to slide past one another horizontally, producing strike-slip faults.

Fault

A fracture in rock along which displacement or movement has taken place.

Fault Plane

The planar surface along which fracture displacement occurs.

Hanging Wall

The block of rock situated directly above an inclined fault plane.

Footwall

The block of rock situated directly below an inclined fault plane.

Normal Fault

A fault produced by tensional stress in which the hanging wall moves downward relative to the footwall.

Reverse Fault

A fault produced by compressional stress in which the hanging wall moves upward relative to the footwall.

Thrust Fault

A low-angle reverse fault formed under compressional stress.

Strike-Slip Fault

A fault produced by shear stress in which rock blocks slide horizontally past each other with minimal vertical displacement.

Transform Fault

A large strike-slip fault that accommodates motion along tectonic plate boundaries (e.g., San Andreas Fault).

Fold

A permanent bend in layered rock produced by ductile deformation under compressional stress.

Axial Plane

An imaginary plane that divides a fold symmetrically or asymmetrically into two halves.

Limb

One of the two sloping sides or flanks of a fold.

Anticline

An arch-shaped fold formed by compressional stress in which the oldest rock layers are located at the center.

Syncline

A trough-shaped fold formed by compressional stress in which the youngest rock layers are located at the center.

Monocline

A step-like, one-sided bend or fold in otherwise horizontal rock strata.