Card Set Information
Flash cards for geology
the maximum clast size transported
the total quantity of sediment carried
Decrease in water velocity affects sediment transport
Competence reduced, sediment drops out.
Boulders, then gravels, then sands fill channel bottoms.
Sands form inside banks (point bars).
Silts and clays drape floodplains.
Stream flow begins as scattered _______
Water flow that occurs when the soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land.
Dendritic Drainage Pattern
Branching or tree-like
Common in regions of uniform material
Radial Drainage Pattern
Draining in all directions away from a point
Found at the perimeter of a high region or feature(mesa, peak, or mountain, etc.)
Rectangular Drainage Pattern
Channels aligned primarily in two directions
Common in gently sloped areas of orthogonally jointed rocks
Trellis Drainage Pattern
Trunk stream flows through resistant rocks,tributaries flow between ridges
Common where surface alternates between erodible and resistant materials
Parallel Drainage Pattern
Several streams with parallel courses
Common in surface with uniform slope
Area of land that drains into a stream
Land areas drain into a trunk stream or body of water
The amount of water flowing in a channel
Volume of water passing a point per unit of time
Multiply cross-sectional area x average water velocity
D = Ac x va
The energy of flowing water is from mass and gravity
Streams convert potential energy (PE) to kinetic energy(KE). KE (e.g., fast water flow) lifts and moves solids
the“sandblasting” of rock by particles in fast moving water
Larger particles roll, slide, and bounce along the bottom
Moves by saltation.
Fine particles (silt and clay) in the water
Movement of solid particles
High discharge—Large cobbles and boulders may move.
Low discharge—Large clasts are not moved.
Change in elevation per distance flowed
The lowest point to which a stream can erode
Velocity drops to zero when it reaches base level.
Ultimate base level is sea level.
A lake is a local or temporary base level.
A ledge of resistant rock may define temporary base level
Valleys and Canyons / Base Level Rises
Stream flow slows, and the valley become filled with more sediment.
Valleys and Canyons / Base Level Falls
Stream flow quickens, and the incision of channels may leave stranded terraces.
Gradient is so steep that water cascades or free falls.
Scours a deep plunge pool.
Basal erosion leads to collapse of overlying rocks.
Temporary base levels.
Trunk stream consists of many interfingering channels
Sediment load is very high and channel is very shallow
Abundant coarse sediment moves during floods.
Sediment is deposited, chokes channel in normal flow.
Weaving channels create ephemeral sand and gravel bars.
The channel is modified during periods of flood
Fast part of current swings back and forth
Momentum increases during flood, erodes outside bank
Forms when a stream enters standing water.
Stream divides into a fan of distributaries.
Velocity slows; sediment drops out.
One stream captures the flow of another.
A stream with vigorous headward erosion and steeper gradient intercepts a stream with gentler gradient.
The captured stream flows into the new stream.
Tectonic uplift may raise a region that has an entrenched stream.
If erosion keeps pace with uplift, the stream remains in its channel.
If the rate of uplift exceeds erosion by the stream, drainage changes.
Evaluating Flood Hazards
A 100-year flood means 1% risk of such a flood in 1 year.
Groundwater resides in subsurface pore spaces.
Pores are open spaces within any sediment or rock.
The total volume of open space.
Geologic materials exhibit a wide range of porosities.
Originally formed with the material.
Voids in sediment
Vesicles in basalt
The ease of water flow due to pore interconnectedness.
Highly _____ material allows water to flow readily.
Sediment or rock that transmits water easily.
Impermeable or low permeability sediment or rock that hinders water flow.
An aquifer that intersects the surface
In contact with the atmosphere
An aquifer beneath an aquitard
Isolated from the surface
Less susceptible to pollution
Above the water table, pores are mostly filled with.
Below the water table, pores are filled with water
Specific measurement of liquid pressure above a geodetic datum
Measured by piezometer
Determined by measuring the hydraulic head. Flow always moves from a high to a low hydraulic head
Groundwater Flow / Recharge Areas
Groundwater infiltrates through _____ areas
Groundwater Flow / Discharge Areas
Groundwater exits the substance through ____ area.
An equation that predicts the volume of water passing through an area of an aquifer at any given time
Q = KA(h1 – h2)/j
Q = Discharge volume (m3/day).
K = Hydraulic conductivity (m/day).
(h1 – h2)/j = Hydraulic gradient (m/m or dimensionless).
A = Cross-sectional area perpendicular to flow (m2).
Natural groundwater outlets
Cone of Depression
A downward-pointed conical-shaped surface
Steepest near the well; flattens with distance
The cone may expand outward with continued pumping
A small well creates a small cone.
A large well creates a large cone.
Water is heated to the boiling point in a vertical spring.
Pressure exerted by the water column prevents boiling.
Some water escapes and pressure is reduced.
The water boils, turns to steam, and erupts as a geyser.
The cycle repeats after the emptied chamber is refilled
Water in pore space holds grains apart.
When groundwater is removed:
Sediment grains compress; pore spaces collapse.
The land surface cracks and sinks.
Failing Septic Systems
Should effectively accept liquid wastes from your house and prevent biological and nutrient contaminants from getting into your well or nearby lakes and streams.
Any, time these things do not happen, the system is failing.
Most remedial strategies include removing the source.
Pump and treat.
Volatilize and vaporize.
Utilizes bacteria to clean groundwater
Develop when groundwater dissolves limestone
Formation of Karst Landscapes
Establishment of the water table in limestone
Development of a cave network via dissolution (Dissolution maximized near the water table)
Thick masses of recrystallized ice.
Presently cover ~10% of Earth.
Forming a Glacier
Cold local climate (polar latitudes or high elevation).
Snow must be abundant; more snow must fall than melts.
Snow must not be removed by avalanches or wind.
Flow from high to low elevation in mountain settings
Vast ice sheets covering large land areas.
Ice flows outward from thickest part of sheet.
Two major ice sheets remain on Earth
: Greenland, Antarctica
Basal Sliding / Movement of Glacier
Significant quantities of meltwater forms at base of glacier.
Water decreases friction, ice slides along substrate.
Plastic Deformation / Movement of Glacier
Occurs below about 60 m depth.
Grains of ice change shape slowly.
New grains form while old grains disappear.
Crevasses form at surface—upper zone too brittle to flow.
Zone of Accumulation
Area of net snow addition.
Colder temperatures prevent melting.
Snow remains across the summer months.
Zone of Ablation
Area of net ice loss.
The leading edge of a glacier.
Ice always flows downhill, even during retreat.
Toe Position: Accumulation = Ablation
The glacial toe stays in the same place.
Toe Position: Accumulation > Ablation
The glacial toe advances.
Toe Position: Accumulation < Ablation
The glacial toe will retreat upslope.
Bowl-shaped basins high on a mountain
Form at the uppermost portion of a glacial valley.
Freeze-thaw mass wasting chews into the cirque headwall.
After ice melts, the cirque often becomes a tarn (lake).
A “knife-edge” ridge.
Formed by two cirques that have eroded toward oneanother
A pointed mountain peak.
Formed by three or morecirques that surround thepeak
Glacial erosion creates a distinctive trough.
Compare to V-shaped fluvial valleys.
The intersection of a tributary glacier with a trunk glacier
Trunk glacier incises deeper into bedrock.
Troughs have different elevations.
A waterfall results.
U-shaped glacial troughs flooded by the sea.
Accentuated by isostatic rebound.
Unsorted debris deposited by a glacier.
Forms along the flankof a valley glacier
Mid-ice moraine from merging of lateral moraines.
Sediment dropped by glacial ice.
Consists of all grain sizes—boulders to clay.
Boulders dropped by glacial ice.
These rocks are different from the underlying bedrock.
Often, they have been carried long distances in ice.
Sediments from an oceanic glacier
Calving icebergs raft sediments away from the ice.
Melting icebergs drop stones into bottom mud.
Sediment transported by meltwater.
Muds are removed.
Sizes are graded and stratified.
Grains are abraded and rounded.
Glaciers produce abundant amounts of fine sediment.
Strong winds over ice blow the rock flour away.
Deposits are unstratified and distinct in color.
Long, aligned hills of molded lodgment till
Asymmetric form—steep up-ice; tapered down-ice.
Commonly occur as swarms aligned parallel to ice-flowdirection.