The Natural Environment Exam 3

Aggradation

Increase in land elevation due to the deposition of sediment

Asthenosphere

Region of the upper mantle just below the lithosphere; the least rigid portion of Earth’s interior and known as the plastic layer, flowing very slowly under extreme heat and pressue

Bed Load

Coarse materials (gravel, pebbles) that are transported along the bed of a stream by rolling (traction, sliding, saltation)

Braided Channel

Channel with a series of shallow, interconnected threads that subdivide and rejoin repeatedly around small islands

(Form due to oversupply of sediment)

Floodplain

Flat land adjacent to a stream that experiences recurrent flooding

Helical Flow

Spiraling like flow through meander bends

(Superelevation of water surface and greater pressure at outer bank)

Magma

Molten rock from beneath Earth’s surface

• Fluid, gaseous, under tremendous pressure

• Either intruded into existing crustal rock or extruded onto the surface as lava

Moraine

Mound or ridge of unsorted rock debris left behind by a glacier

Perennial Stream

Continuous flow all year during normal periods of downfall

Point Bar

Inner portion of meander band that experiences slowest water velocity and receives deposited sediment

Seafloor Spreading

Occurs at mid-ocean ridges, where tectonic plates separate and new oceanic crust is created through volcanic activity

Stream Competence

Stream’s ability to more particles of a specific size

(Function of velocity of flow and energy available to suspend particles

Subduction

Where one tectonic plate is forced beneath another leading to significant geological activity

Viscosity

A measure of a fluid’s resistance to flow, often described as its “thickness”

Volcanic Arc

A chain of volcanoes parallel to subduction zone that forms as an oceanic plate subducts under a continental plate

• Crater Lake

Water Table

Boundary that separates saturated zone below from the unsaturated zone above

Water Shed

Area of land that drains into a specific river or stream

Hydrologic Cycle

Interaction between the atmosphere, hydrosphere, lithosphere, and how they shape Earth’s surface

(Continuous movement of water on, above, and below Earth’s surface)

Groundwater

Water that fills spaces between grains in soil or fills fractures in rock

River

Topographically low area of land that collects surface water and interacts with ground water to transport water and eroded materials

3 Main River Processes

Transportation, erosion, deposition

Sediment Transport

Amount of material transported depends on topographic relief, type of material, climate, vegetation, and human activity in watershed

Stream Competence Vs. Capacity

Competence- Ability to move particles of a SPECIFIC size

Capacity- TOTAL amount of sediment a stream can transport, NO MATTER SIZE

Dissolved Load

Material that is carried in solution by a stream

(Chemical solution from minerals and salts)

Suspended Load

Fine-grained particles (sand, silt, clay) that are held up by turbulence in a stream

Intermittent Stream

Stream that only flows during part of the year

(Usually associated with seasons)

Ephemeral Stream

Only flows during and immediately after periods of rainfall

Baseflow

Portion of streamflow that comes from groundwater seepage into a channel; contributes to perennial streams

Straight Channel

• Don’t usually occur naturally

• Most often a result of anthropogenic activities

• Typically occurs when streams are channelized

• Used in urban and rural areas

Braided Channels Characteristics

• Excess amount of sediment

• If bed exceeds capacity, sediments build up and the stream channel does as well through deposition

Meandering Channel Features

Point bar, Cut bank, oxbow lakes, Cutoofs

Movement of Water

Primary Flow (Downstream)

Secondary Flow (Side to Side)

Sheet flow

Initial overload flow in the form of a continuous film of water that moves downslope

Rills

Narrow, small-scale downhill grooves in topsoil resulting from erosion by sheetflow

Gullies

Larger incisions that erode sharply into soil, typically on a hillside, that resembles a large ditch or small valley

Alluvial Terrace

Remnant of earlier floodplains that existed at an earlier time when a stream was flowing at a higher elevation before its channel down cut to create a new floodplain at a lower elevation

River Delta

Landform at the mouth of a river where it flows into an ocean, sea, or lake

• Formed from deposition of sediment. Flow from river slows resulting in increased ability to transport materials

• Important ecologically (wetlands) and can protect human development and inland areas from storms

Glacier

Large natural accumulation of ice that originates on land and flows slowly due to stressed induced by weight and gravity

• Form by continual accumulation of snow and crystalizes under its own weight into an ice mass

• Not stationary, moves slowly in streamline patterns

Alpine Glacier

Long, narrow glacier that forms on slopes of mountains

Valley Glacier

Type of alpine glacier that fills a valley, initially formed by streams

Continental Glacier

Continuous mass of unconfined ice covering at least 19500 mi²

• OCCURS ON A MUCH LARGER SCALE THAN INDIVIDUAL GLACIERS

Isostatic Depression

Heavy weight of glaciers causes Earth's crust to sink

Isostatic Rebound

After continental glaciation has receded, crust rebounds and land rises since ice is no longer weighing on it

Glacial Drift

Silt, clay, sand, gravel, and boulders left behind by retreating glaciers

Terminal Moraine

Eroded debris dropped at glacier’s farthest extent

Lateral Moraine

Forms along lobes of glacier

Kettle

Lake formed by retreating blocks of ice that melted and left behind steep-sided hole

Plains

Broad, relatively flat land

Exogenic Processes

External processes that put into motion air, water, and ice

• Carve, shape, reduce landscape

Endogenic Processes

Internal processes that produce flows of heat inside Earth

• Moving, warping, and breaking landscape

Continental Drift

Movement of Earth’s continents relative to each other

Pangea

Continents had once formed a single landmass before breaking apart

Seafloor Spreading Hypothesis

• Hess suggested that along a crack at the bottom of the Atlantic, the ocean floor separates along the crack and new material is added

1960’s

• Tremendous revolution in geologic thinking

• Emergence of theory of plate tectonics

Lithosphere

Broken into plates separated by

• Divergence

• Convergence

• Transform Boundaries

Tectonic Cycle

• Melted Asthenosphere flows upward as magma

• Cools to form new ocean floor (Lithosphere)

• New oceanic lithospheric diverges from zone of formation atop asthenosphere

• When slab of oceanic lithosphere collides with another slab, colder and denser slab SUBDUCTS under hotter and less dense slab

• Subducted slab is reabsorbed into the mantle

Why Does One Plate Subduct Beneath Another?

The plate that is older, colder, and more dense will sink

Divergent Plate Boundaries

2 Plates move away from each other, and where new oceanic crust and lithosphere are created

Seafloor Spreading Process

• Convection currents pull solid crust apart

• Magma fills the opening to create new crust

• As new material forms, it pushes older seafloor away

Rift Zones

Geological feature where the Earth's lithosphere is being pulled apart, leading to the formation of new crust as magma rises to the surface.

Collision Boundary

When 2 plates with continental Lithosphere collide

Transform Boundaries

Where 2 plates slide past one another horizontally

• San Andreas

Basaltic Magma

• Gas Content: Low

• Temperature: High

• Viscosity: Low

• Type of Eruption: Effusive (non-eruptive)

Andesitic Magma

Gas Content: Intermediate

Temperature: Warm

Viscosity: Intermediate

Type of Eruption: In-between

Rhyolistic Magma

Gas Content: High

Temperature: Cool

Viscosity: High

Type of eruption: Explosive

Plate Tectonics

Theory that proposes Earth’s Lithosphere (crust) is divided into plates that move around on the top of the Asthenosphere

Oxbow Lake

Laurentide Ice Sheet

Massive sheet of ice that covered large parts of North America between 95,00 and 15,000 years ago

• Continental glacier that shaped most of Illinois

Oxbow Lake

A former bend on a meandering river that has been cutoff

Plutonic Rocks

• Formed from crystallization of molten magma deep within the Earth’s crust

• Cool slowly over thousands of years, allowing large mineral crystals to develop

Drainage Divide

Line separating neighboring watersheds

• Divides lie along topographical high points in hilly areas

Aphanitic Rocks

Igneous rocks with microscopic crystals

Igneous Rocks

Molten material, such as magma and lava, solidifies and crystalizes to form these rocks

Convection

Method of heat transfer in the Asthenosphere, the upper portion of Earth’s mantle, that drives plate tectonics

Alluvium

Deposit of clay, silt, sand, gravel, and mineral fragments by flowing streams

Explosive Eruption

Violent gas release and fragmentations

Effusive Eruption

Gentle flow of lava