Geology - Ch. 5-9

Magma

Molten rock that usually contains some crystals and varying amounts of dissolved gases

Lava

Erupted magma

Viscosity

A measure of a fluid's mobility

Factors Affecting Magma Viscosity

• Silica: More silica = more viscous

• Temperature: Cooler temp = more viscous

Basaltic Lava

• Silica poor, low gas content, higher melting temperature

• Very fluid, flows in thin, broad sheets or ribbons

• Fast flowing, covers a lot of area

Felsic Lava

• Silica rich, high gas content, lower melting temperature

• Very thick

• Slow flowing, covers a small area

Lava Tubes

A natural tunnel within a solidified lava flow, formerly occupied by flowing molten lava

Pillow Lavas

Lava that solidifies in an underwater environment and develops into a structure like a pillow

Volatiles

Gaseous components of magma dissolved in the melt; will readily vaporize (form a gas) at surface pressures.

Pyroclastic Materials

The volcanic rock ejected during an eruption, including ash, bombs, and blocks. Also called tephra

Volcanic Ash

Fine, glassy fragments

Tuff

Fused ash

Lapilli (Cinders)

Walnut-sized pyroclastic material

Bombs

Ejected as hot lava >2.5 inches in diameter. Ejected semi-molten so they take on a streamlined shape as they hurtle through the air

Blocks

Hardened or cooled lava >2.5 inches in diameter

Pumice

Light gray or pink porous rock from frothy andesitic and rhyolitic lava

Scoria

Reddish-brown porous rock from frothy basaltic lava

Shield Volcano

A low, flat, gently sloping volcano built from many flows of fluid, low-viscosity basaltic lava

Cinder Cone

A steep, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs piled up around a volcano's opening

Flood Basalts

Form when lava flows out of long cracks in Earth's crust

Lava Plateaus

Landform produced by repeated flood basalts

Composite Cone

A volcano composed of both lava flows and pyroclastic material

Pyroclastic Flow

The flow of ash, cinders, bombs, and gases down the side of a volcano during an explosive eruption

Lava Dome

Forms inside a composite cone

Lahar

An avalanche of volcanic water and mud down the slopes of a volcano

Volcanic Gases

Gases emitted include water vapor, carbon dioxide, and sulfur gases; can be poisonous

Volcanic Neck

Solid igneous core of a volcano left behind after the softer cone has been eroded

Caldera

A large crater caused by the violent explosion of a volcano that collapses into a depression

Weathering

The physical breakdown and chemical decomposition of rock

Mass Wasting

The transfer of rock and soil downslope under the influence of gravity

Erosion

The physical removal of material by water, wind, ice, or gravity

Mechanical Weathering

The type of weathering in which rock is physically broken into smaller pieces

Chemical Weathering

The type of weathering in which rock is broken down by chemical reactions and transformed into new minerals

Frost Wedging

The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices

Talus Slopes

An accumulation of rock debris at the base of a cliff

Salt Crystal Growth

A mechanical weathering process in which salt crystals growing in cracks and pores push rock pieces apart

Sheeting

A mechanical weathering process that is characterized by the splitting off of slablike sheets of rock.

Exfoliation Domes

Large, dome-shaped structure, usually composed of granite, formed by sheeting

Formation of Acid Rain

Carbon dioxide in the air combines with water to form carbonic acid, which dissolves halite

Hydrolysis

Hydrogen ion in water attacks and replaces another ion in the mineral altering it into a clay mineral

Clay Minerals

Silicate minerals produced by hydrolysis of other silicate minerals. Occur as clay-sized particles and are very stable under surface conditions

Spheroidal Weathering

Any weathering process that tends to produce a spherical shape from an initially blocky shape

Soil

The product of physical and chemical weathering and is a mixture of eroded rock, decaying organic matter, water, air and billions of living organisms

Humus

Decaying organic matter from the remains of plants or animals

Regolith

Loose rock rubble accumulated at the surface over solid rock

Topsoil

Mixture of humus, clay, and other minerals that forms the crumbly, topmost layer of soil. Supports life

Laterite Soil

A red, highly leached soil type found in the tropics and rich in oxides of iron and aluminum

Soil Erosion

Movement of soil components, especially topsoil, from one place to another, usually by wind, flowing water, or both. This natural process can be greatly accelerated by human activities that remove vegetation from soil

Sedimentary Rock

A rock that forms from compressed or cemented layers of sediment

Deposition

Process in which sediment is laid down in new locations

Detrital Sedimentary Rock

Sedimentary rock made up of the solid particles (detritus) of preexisting rocks

Chemical Sedimentary Rock

Sedimentary rock that forms when minerals crystallize out of a solution to become rock

Organic Sedimentary Rock

Sedimentary rock that forms from the remains of plants or animals

Shale

Soft, finely stratified sedimentary rock that formed from consolidated mud or clay and can be split easily into fragile slabs

Sandstone

A sedimentary rock formed by cementing grains of sand over time

Well Sorted

Grains are the same size

Poorly Sorted

Grains are a range of sizes

Long Transport

Grains are well rounded and well sorted. Composed of only quartz

Short Transport

Grains are angular and poorly sorted. Composed of quartz, feldspar, and ferromagnesian minerals

Limestone

Composed of CaCO3, most abundant sedimentary rock, includes coquina, coral reefs, chalk, and travertine

Chert

SiO2, inorganic precipitate of microcrystalline quartz deposited directly from water

Evaporites

Sedimentary rocks formed from minerals left after water evaporates

Coal

Composed of organic matter deposits in stagnant swamps where there was incomplete decay because of a lack of oxygen

Diagenesis

Chemical, physical, and biological changes that take place after sediments are deposited

Lithification

The process that converts sediments into solid rock by compaction or cementation

Compaction

The process that presses sediments together

Cementation

The process in which minerals precipitate into pore spaces between sediment grains and bind sediments together to form rock

Sedimentary Facies

The change in rock type and sedimentary environment within a single sedimentary layer

Strata

Layers of sedimentary rock

Bedding Planes

Separate strata

Sedimentary Structures

Provide information about the environment of deposition

Ripple Marks

Evidence of a current oscillating back and forth; forms symmetric peaks. Could be caused by wind or water

Graded Beds

A sorting of grain size within a sedimentary layer from one side to the other

Mud Cracks

Evidence that the area was an ancient soil zone; form when clay in the soil zone expands when wet, then contracts when dry

Cross Bedding

Evidence of a current in one direction; form asymmetrical peaks. Ancient sand dunes or river bed

Fossils

Preserved remains of once-living organisms often found in sedimentary rock

Metamorphism

The changes in mineral composition and texture of a rock subjected to high temperatures and pressures within the Earth

Metamorphic Rock

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions

Agents of Metamorphism

Increased temperature (most important); Increased pressure (stress); Hot water. Cause the chemical bonds within minerals of the original rock to break and then form new minerals without melting of the original rock

Sediment Burial

Burial to higher temperatures found deeper in the earth; raises the temperature and pressure of rocks to metamorphic conditions

Tectonic Burial

When one block of crust is forced over another, the lower one heats to a temperature associated with its new depth

Magma Intrusion

Raises the temperature of rock by altering the local geothermal gradient. This metamorphoses adjacent rock and is referred to as contact metamorphism

Confining Pressure

Pressure increases with increased depth in the Earth because of the increased load of the rock; pressure is equal in all directions so it does not deform the rock

Mountain Building

occurs when two plates collide together and create forces that cause folding and faulting of rock layers

Differential Stress

Caused by directional tectonic forces. The forces are greater in one direction than another, causing the rock to be folded and deformed

Foliated

The metamorphic rock texture in which mineral grains are arranged in planes or bands in response to stress

Hydrothermal Metamorphism

Occurs when very hot water reacts with rock, altering its mineralogy and chemistry

Nonfoliated

The texture of metamorphic rock in which the mineral grains are not arranged in planes or bands. Mass of interlocking crystals

Slaty Cleavage

A type of foliated texture where rock splits along closely spaced planar surfaces

Schistosity

A type of foliated texture where platy minerals create a layered structure

Gneissic Texture

A type of foliated texture with a banded appearance

Low Grade

Type of metamorphism occurring at low temperatures and pressures

High Grade

Type of metamorphism occurring at high temperatures and pressures

Slate

A type of foliated metamorphic rock that is very fine grained, has slaty cleavage, and is generated from low grade metamorphism of shale

Schist

A type of foliated metamorphic rock that is medium to coarse-grained and predominately composed of platy minerals such as micas

Gneiss

A type of foliated metamorphic rock that is medium to coarse-grained with a banded appearance. It is generated from high grade metamorphism of shale.

Quartzite

A nonfoliated metamorphic rock produced from the metamorphosis of quartz sandstone

Marble

A nonfoliated metamorphic rock produced from the metamorphosis of limestone

Migmatite

A rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when light-colored non-ferromagnesian minerals melt and then crystallize, while the dark ferromagnesian minerals remain solid

Relative Dating

Method that determines the order in which formations deposited, but does not reveal exactly when they were deposited