Geology ch. 12, 16, 17, 20

A stream begins at an elevation of 200 meters and flows a distance of 400 kilometers to the ocean? What is the average gradient?

0.5 m/km

Base Level

3/8/20176Three Ways That Streams Transport Their LoadBed LoadStream Capacity and Competence•Capacity:-Maximum load a stream can transport-Increasing discharge increases capacity of stream•Competence: -Indicates the maximum particle size a stream can transport-Determined by the stream's velocity-Greater velocities can carry larger particles in suspension and as bed loadStreams with higher discharge can carry a greater sediment loadBase Level•Base level is the lowest point to which a stream can erode•Two general types of base level:-Ultimate (sea level)-Local or temporary (resistant rock layers, lakes, dams, etc

An aquifer is...

A saturated, porous, and permeable layer or stratum

Headward Erosion

A stream can lengthen its course two ways:-Build a delta at its mouth-Headward erosion•Headward erosion may result in stream piracy -the diversion of the drainage of one stream into another

How does wave refraction affect the crest and trough orientations of incoming waves along a beach?

As the waves move into shallower water, the angle between the wave crests and shoreline decreases and the crests become more parallel with the shoreline

Which one of the following statements correctly describes how stream terraces can form?

Base level drops, the stream actively downcuts, and the former floodplain is left well above the present elevation of the stream.

How a Stream Transports Material

Bed load:-Coarser particles moved by rolling and sliding along the stream bed•Suspended load:-Finer particles carried in suspension•Dissolved load:-Dissolved chemical substances such as HCO3-. Ca2+, Cl-, K+, Mg2+, SO4 2+

How does a water gap form?

Both antecendent and superposed streams can create water gaps.

The common, rock-forming mineral __________, which comprises the rock _______________, most readily dissolves in slightly-acidic groundwater?

Calcite / limestone

Which of the following is not part of the hydrologic cycle?

Calcium carbonate dissolving in soil water and groundwater

Which of the following describes the total sediment load transported by a stream?

Capacity

Stream Capacity and Competence

Capacity:-Maximum load a stream can transport-Increasing discharge increases capacity of stream•Competence: -Indicates the maximum particle size a stream can transport-Determined by the stream's velocity-Greater velocities can carry larger particles in suspension and as bed load

Atlantic and Gulf Coasts

Characteristics:-Tectonically stable-Broad, gently sloping coastal plains-Barrier islands-Estuaries•Problems:-Submergence -Erosion-Urbanization of barrier islands

Contamination of wells by saltwater intrusion is commonly a problem in _______________

Coastal areas

Which of the following describes the changes likely to occur in an unconfined aquifer around a pumping well?

Cone of depression forms around the well

Heat from the core is transferred through the mantle to the base of the crust mainly by __________

Convection

A dam and reservoir are constructed on a graded river. What will happen?

Deposition upstream from the dam; channel downcutting below

Depositional Features

Depositional features are related to beach drift and longshore currents:-Spits-Baymouth bars-Tombolos-Barrier island

Which of the following factors do not influence stream turbulence and average velocity?

Dissolved load and water temperature above freezing

At the head of a delta, the major channel splits into smaller channels that follow different paths to the sea. These smaller channels are known as ________.

Distributaries

What is the relationship between drawdown and the cone of depression associated with a pumping well?

Drawdown is the distance between the original water table and the water level in the well.

Effect Of Earth's Rotation On Gravity

Earth's equatorial bulge results in greater gravitational acceleration at the poles (9.83 m/s2) than at the equator (9.78 m/s2) for two reasons: -Centrifugal (rotational) force that counteracts gravity is greater at equator than at the poles-Earth's surface is further from the center of gravity at the equator than at the poles•As a result, fisherman who weighs 200 pounds at the north pole would only weigh 199 pounds at the equator

Which one of the following features is not characteristic of a submergent coastline?

Elevated, wave-cut terraces

Other Factors That Affect Gravity

Elevation:-Higher elevations puts Earth's surface further from center of gravity (center of the Earth) so that gravity decreases•Density differences of rocks below Earth's surface:-Higher density rocks below the surface increase gravitational attraction locally

As P waves pass from the mantle into the outer core, velocities increase abruptly.

False

Earth's radius is slightly longer at the pole, but shorter at the equator.

False

Gradients usually increase downstream in a major river system.

False

Tidal flats are mostly submerged during ebb tides.

False

Erosional Features

Features along coasts undergoing erosion include:-Wave-cut cliffs-Marine terraces-Wave-cut platforms-Sea caves-Sea arches-Sea stacks

A _________ tide is a tidal current flowing through an inlet into a bay or estuary.

Flood

Floods

Floods are the most common and destructive geologic hazard:-Stream is unable to accommodate dramatic increase in discharge-Water overflows banks onto flood plain•Result from naturally occurring and human-induced factors

Factors That Control the Way a Stream Behaves

Gradient•Channel cross-sectional area (ft2or m2)•Average velocity of water flow ( ft/sec or m/sec)•Discharge (ft3/sec or m3/sec)•Sediment load (kg/m3

After ice sheets and glaciers, which of the following reservoirs contain(s) the next highest percentage of the Earth's freshwater?

Groundwater

Which of the following statements regarding the mapping of the water table is INCORRECT?

Groundwater flow lines parallel the water-table contour lines

Which of the following characteristics are found in all good aquifers?

High porosity and high permeability

For unconfined aquifers, what hydrologic factor is approximated by the slope of the water table?

Hydraulic gradient

Stream Erosion

Increasing the stream velocity can result in erosion of the channel:-When the flow of water is sufficiently strong, it can dislodge and lift particles in the channel•The streams velocity can increase due to:-Increasing discharge such as after a heavy rainfall -Narrowing of the stream channel. 3/8/20175Stream Erosion•Increasing the stream velocity can result in erosion of the channel:-When the flow of water is sufficiently strong, it can dislodge and lift particles in the channel•The streams velocity can increase due to:-Increasing discharge such as after a heavy rainfall -Narrowing of the stream channelLandslide Narrows Stream Channel, Increasing Velocity; Resulting Erosion Removes Landslide Debris Bridge Piers Increase Velocity And Sometimes Erosion Next To PiersStream Erosion•A sufficiently strong flow of water can dislodge and lift particles in the channel•Loosely consolidated particles are lifted by:-Abrasion-Dissolution•Stronger (faster) currents lift particles more effectively

How does urbanization (paving, etc.) affect runoff and infiltration in a small, previously forested, drainage basin?

Infiltration decreases while runoff increases

____________ are coastal structures designed to keep tidal and harbor inlets from shifting location or filling with sand.

Jetties

What does the following figure best illustrate?

Karst topography

Streamflow

Laminar flow:-Characteristic of slow-moving streams-Streamlines in roughly parallel paths•Turbulent flow:-Characteristic of faster-moving streams-Streamlines erratic with swirling motion-May exhibit whirlpools and eddies

The Earth's Magnetic Field

Liquid iron in the outer core is stirred into convective motion by Earth's internal heat•Circulation of liquid iron in outer core produces electric currents•These electric currents, in turn, generate the Earth's magnetic field

___________ currents move offshore sand and water parallel to the beach.

Longshore

Earth' Internal Heat Engine

Major processes that have contributed to Earth's internal heat:-Heat released by colliding particles during formation of Earth 4.57 billion years ago-Heat released as iron crystallized to form the solid inner core of early Earth-Heat emitted by radioactive decay of isotopes-The Moon-forming impact

Which of the following terms does not belong with the other terms?

Marine terrace

The ___________ is the seismic discontinuity that forms the boundary between the crust and mantle.

Moho

Swash and backwash describe...

Movements of water and sand as waves wash up and back again on a beach

Two Types Of Stream Valleys

Narrow valleys:-V-shaped -Stream downcutting toward base level-Features often include rapids and waterfalls•Wide Valleys:-Stream is near base level-Downward erosion is less dominant-Stream energy is directed from side to side forming a floodplain

Which of the following features characterize wide streams and valleys?

Natural levees and broad floodplains

Which one of the following statements is true concerning natural levees?

Natural levees are formed where the coarsest sediments are deposited adjacent to the channel during floods

Which of the following statements about the 'D' layer is false?

Occurs directly below continental and oceanic crust

Where is stream erosion concentrated along a meandering stream?

On the outer bank of a meander bend

For a passing wave, the depth below which the motion of water particles become negligible is equal to...

One-half the wavelength

The __________ of the Earth does not transmit S waves.

Outer core

A(n) __________ is an abandoned, cutoff, meander loop.

Oxbow lake

Which of the following is good evidence for a solidified, inner core?

P waves are faster in the inner core than in the outer core

Pacific Coast

Parts of Pacific coast are emergent:-Narrow beaches-Steep bedrock cliffs-Wave-cut platforms-Elevated marine terraces•Problems:-Narrowing of beaches due to loss of sediment (damming of rivers traps sediment load in reservoirs)-Beaches gone, so cliffs erode faster

_____________ is probably closest in chemical composition to the upper mantle.

Peridotite

What force pushes groundwater from pore to pore below the water table?

Pressure gradient or hydraulic gradient

What type of stream pattern develops only on growing mountains like volcanoes or where the land surface is tectonically doming upward?

Radial

The Geoid

Sea level is not uniform everywhere, but varies in height due to density differences of materials below Earth's surface (gravity effect)•The geoid is a representation of sea level and is distorted relative to a perfect spheroid formed solely by Earth's rotation. Differences in the height of the geoid, relative to the perfect spheroid, are caused by density differences below Earth's surface:-If underground density anomalies are near the surface, geoid anomalies are narrow-If density anomalies are deep, then geoid anomalies are very broad

A ____________ is an isolated, exposed remnant of bedrock that is now offshore.

Sea stack

_____________ are built behind a beach and serve to protect structures from strong waves and surges.

Seawalls

Characteristics of Barrier Islands

Seaward side:-High energy wave and current action-Fairly straight shoreline-Sand on beach typically clean, well sorted and rounded with ripples and cross bedding•Lagoon side:-Quieter, low energy, occasional storm washoverdeposits-Irregular shoreline-Tidal marsh mud and peat deposits

Which of the following make up the suspended loads of most rivers and streams?

Silt and clay-sized, detrital grains

Which of the following rock types would have the largest capacity to naturally remove sewage pollutants?

Slightly clayey sand

Which of the following did not contribute to Earth's internal heat?

Solar radiation from the early sun

________ are the maximum-amplitude tides produced when the Sun, Earth, and Moon are aligned. Selected Answer: Correct

Spring tides

A ________ is the icicle-like speleothem that grows down from the roof of a cavern.

Stalactite

A __________ refers to the broad dome of water moving with the eye and frontal portion of a hurricane.

Storm surge

Large estuaries are more common on a(n) ___________ coastline.

Submergent

Which of the following statements about barrier islands is false?

The beach side of barrier islands is identical to the lagoon side in terms of overall appearance, types of sediments, and vegetation

Refraction

The bending of seismic waves while passing through the Earth is called refraction

Which of the following statements is INCORRECT with regard to the water table?

The level of the water table never changes regardless of the time of year

Stream Channels

The size and shape of a channel cross section is a function of several factors:-Stream gradient (slope)-Surrounding rock type-Discharge•The most efficient channel is one with the least perimeter for its cross-sectional area

Excessive groundwater withdrawal can lead to which of the following results?

The water table drops or declines in elevation

Seismic Tomography

Three dimensional model of Earth's interior based on seismic imaging•Requires seismic records from many (thousands) of different earthquakes•Identifies regions where P-and S-waves are faster or slower than average•Velocity variations of seismic waves attributed to variable temperatures and other material properties:-Higher temperatures, slower velocities-Lower temperatures, greater velocities

A natural sand bar or low, sand ridge that connects one island to another island or to the mainland is called a __________.

Tombolo

Continental crust is generally thicker than oceanic crust.

True

Differences in the height of Earth's geoid is measured relative to a perfect ellipsoid.

True

In areas underlain by unconsolidated or weakly consolidated strata, lowering of the water table can cause the land to subside.

True

Neap tides are produced when the Moon is at right angles to the line connecting the Earth and Sun.

True

The geothermal gradient is a curve showing the increase of temperature with depth within Earth's interior.

True

The lowest base level for most streams is sea level.

True

Water infiltrates down to the water table from influent streams.

True

The example of seismic tomography illustrated below shows hotter and colder regions of Earth's mantle based on measured variations in __________

Velocities of S waves

An artesian well is one in which...

Water rises above the top of the aquifer without any pumping

Water movement and sand transport parallel to the beach are fundamentally caused by...

Waves impinging obliquely onto a beach

The Earth's magnetic field originates by...

Weak electrical currents associated with fluid motions in the outer core

Which of the following statements concerning artesian wells is not true?

When the well penetrates the aquifer, the groundwater reverses flow such that the water table drops in the well

Match each of the following questions with the appropriate letter.

Which level indicates the P-wave shadow zone? Correct B. B Which level indicates the zone where no direct P-waves are received? Correct A. A Which level indicates the zone where direct P-waves are received? Correct C. C

Which of the following statements best describes how geysers erupt?

With a slight reduction in pressure, water in a saturated, natural conduit suddenly boils, sending a plume of steam and hot water into the air above the vent.

The water table is...

A boundary between saturated rock below and unsaturated rock above

Which one of the following coastlines would typically have wave-cut cliffs, sea stacks, sea arches, and sea caves?

A coastline where bedrock is vigorously eroded as sea level rises

A perched water table develops when...

A horizontal aquitard above the regional water table prevents downward-percolating water from reaching the main aquifer. Downward percolating water accumulates above the aquitard to form a secondary zone of saturation above the main water table.

Which of the following statements logically explains why parts of some cavern systems are aerated?

A nearby, downcutting stream lowered the water table after the caves had formed.

Water Gap

A water gap is a notch where a river cuts through a ridge that lies in its path•Two possible methods of formation:-Antecedent stream -stream existed before the ridge was formed-Superposed stream -stream lets down upon a preexisting structure

Which one of the following best characterizes the asthenosphere?

A zone of softened peridotite in the upper mantle

The two transition zones in Earth's mantle, one at 400 km and the other at 670 km depths, are characterized by...

Abrupt increases in P- and S-wave velocities due to closer atomic packing of crystal structures in mantle minerals

Which of the following accounts for the largest usage of groundwater in the United States?

Agriculture and irrigation

What type of terrain is characteristic of the drainage pattern shown below?

Alternating weak and resistant bedrock characteristic of folded terrain

Which of the following features are characteristic of downcutting streams and a youthful stage of valley evolution?

Rapids, V-shaped valley, and lots of whitewater

The P-wave shadow zone is largely the result of...

Refraction of P waves crossing the mantle-core boundary

How are spits and baymouth bars formed?

Sand is deposited partly or completely across an inlet or bay by beach drift and longshore currents

Which of the following must result in a lower base level for rivers and streams?

Sea level falls; land rises