Earth Science Test 5

Distinguish between ultimate and temporary or local base level.

Ultimate base level: sea level (the lowest water can go is the sea it came from.) Temporary (or local) base level: a lake, a larger stream, a layer of resistant rock.

What are distributaries?

When on a delta the main channel splits into several smaller streams. It distributes the water from main channel to the delta.

What is a braided stream? What does it indicate about the stream?

When the stream load is greater than its capacity, then a braided stream results. The stream is choked full of sediment and it produces a bunch of little channels within the main channel. The discharge of these streams tends to be highly variable.

List and describe the idealized stages in the development of a river and its valley and discuss several distinguishing characteristics of each stage.

Young: deep, v-shape. Mature: nearly as deep as it will be, starts to widen. Old: broad and wide and flatter.

What term describes all the sediment deposited by a stream?

alluvium.

How is a natural bridge formed in a karst area?

from the collapse of the roof of a cave tunnel.

Draw a cross-sectional diagram of a delta to illustrate the location of the foreset, and bottomset beds.

(in book?)

Name and recognize 4 stream drainage patterns.

(page one of notes)

Where do caves form relative to the water table? Where do speleothems form relative to the water table?

-At or below the water table. -Above the water table in the unsaturated zone.

What do the competence and the capacity of a stream each measure?

-Competence: maximum size particles transported. Depends on the stream's velocity KE= 1/2 mv ^2 -Capacity: maximum load transported. Depends on the stream's discharge. 3. Deposition: occurs when the stream's velocity is reduced. -Heavier particles settle out first resulting in sorting of the transported material. *Both increase tremendously during floodstage, so much so that most of the erosion and transport of material occurs during floodstage.

Describe the effect of retention ponds on the hydrograph of a drainage basin and how they affect dry weather.

-Retention basins (ponds) are partial remedies -they delay the entry of water into the stream run off -they increase the lag time -they decrease the peak discharge -they increase the infiltration of water into the ground. -the water table is maintained higher than it would be otherwise and the dry season discharge is higher than it would be otherwise.

Describe some general factors involved in the formation and development of caves.

-groundwater erosion -created at or below the water table in the zone of saturation. -limestone -the constant dripping water creates things in the limestone called travertine. -cave deposits are called dripstone (formation not possible until it is above the water table in the unsaturated zone) (the cavern must be filled with air.)

Name and describe the 3 types of "work" of streams.

1. Erosion: most occurs during high-flow periods. can be especially rapid if the bed and channel sides are composed of poorly consolidated material. -it typically dominates in the upstream area. -if the stream has a bedrock channel, most of the erosion is by abrasions by its load of sediment. gravel caught in swirling eddies can act like a drill and form potholes. 2. Transportation: of eroded material. -Dissolved load: most dissolved minerals come from ground water. -Suspended load: fine sand, silt, and clay particles and suspension. -Bed load: particles that are too heavy to be carried in suspension and that roll or bounce along the bottom.

Name and describe factors that control stream velocity.

1. Gradient: slope of stream channel. -vertical drop per unit of horizontal flow. 2. Channel Characteristics (size, shape, and roughness): -Friction slows down the water moving in a stream. So, anything that increases the friction (boulders, trees, etc.), decreases the stream velocity, and anything that decreases the friction, increases the stream velocity. 3. Discharge: the volume of water flowing past a point per second.

Describe the 3 "loads" transported by a stream and rank them in order of their importance.

1.Dissolved load: most dissolved minerals come from ground water. 2.Suspended load: fine sand, silt, and clay particles and suspension. 3.Bed load: particles that are too heavy to be carried in suspension and that roll or bounce along the bottom.

Which of the "works" of a stream is more important in each of the 3 "ages"of a stream? Which is more important in the headwaters, middle section, and farthest downstream areas of a stream?

???

Describe what is meant by the drainage basin of a stream? What is a divide?

All the land area that contributes water to a stream. A divide separates 2 drainage basins.

In what kind of rock do most caves form? What acid is more important in cave formation?

Caves form in limestone at or below the water table. Limestone is very susceptible to attack by naturally acidic water.

What is the difference between a delta and an alluvial fan?

Delta: deposited at the mouth of a stream as it enters a lake or the ocean where its velocity is suddenly reduced. The coarser particles (sand) are deposited first. These make up the foreset beds. The smallest particles (silt, clay) are deposited last. These make up the bottomset beds. On a delta the main channel splits into several smaller streams called distributaries. Alluvial fan: a fan or cone shaped accumulation of alluvium deposited where the gradient of a stream is suddenly reduced as it emerges from a mountainous, narrow valley onto a flatter terrain.

Calculate the gradient or discharge of a stream given the appropriate information.

Gradient: (drop) ft./(how far it flows)mi. = (total)ft./mi. Discharge: width (ft) x depth (ft) x velocity (ft/sec.)= discharge

How do the gradient, discharge, width, depth, velocity, and sediment size of a stream change from upstream to downstream?

Gradient: decreases Discharge: increases (in arid regions,the discharge may decrease) Width: increases Depth: increases Velocity: increases sediment size: decreases

What is a hydrograph? How does it change when a stream's drainage basin becomes urbanized? What does this mean in terms of the stream itself and the area it drains?

Hydrograph: a graph measured by time and discharge (rainfall). (page 4 in notes) After urbanization: -fields and forests are replaced with impermeable surfaces, like streets, parking lots, rooftops. -the lag time is decreased and the peak discharge is increased for the same amount of rainfall. -as a consequence, there is a greater chance of flooding. -more water runs off and less water soaks into the ground. -the water table is lowered. -the dry season discharge is decreased.

What river has the world's largest discharge? Where does the Mississippi River rank?

Largest: Amazon River Mississippi: 611,000 ft. ^3/sec.

What will happen in a stream it its base level is lowered? Raised?

Lowered: ? Raised: ?

What is an entrenched (incised meander? What causes it to form?

Rivers that exhibit meandering channels that flow in steep, narrow valleys. Originally, the meanders probably developed on the floodplain of a stream that was relatively near base level. Then, a change in base level caused the stream to begin downcutting. One of two events could have occurred. Either base level dropped or the land upon which the river was flowing was uplifted.

List some characteristics of a karst topography.

The action of acidic water over a large area produces a karst topography . Features include: -caves -disappearing (sinking) streams -springs (where water that has been underground come out naturally at the surface.) -sink holes -Tower karst-form in wet climates where there are thick layers of highly jointed limestone. So much rock is dissolved away that only steep, tall towers are left. -some natural bridges- from the collapse of the roof of a cave tunnel.

Describe how meanders, point bars, and oxbow lakes are formed.

Meanders: streams that transport much of their load in suspension generally move in sweeping bends called meanders. Point bars: Debris acquired by the stream at the cut bank moves downstream where the coarser material is generally deposited as point bars on the insides of bends. Oxbow lakes: an abandoned bend in the shape of a "c."

Describe the formation and location of natural levees, backswamps, and yazoo tributaries.

Natural levees: parallel their channels on both banks. Built by successive floods over many years. Backswamps: The area behind the levee is characteristically poorly drained for the obvious reason that water cannot flow up the levee and into the river. These marshes are formed as a result. Yazoo tributaries: flows roughly parallel to the main stream.