Chapter 16

Uplift

" *Tectonic _* generally causes streams to erode down into the landscape, cutting canyons and steepening the topographic relief."

graded stream

"A channel is stable, attaining a type of dynamic equilibrium, neither eroding nor depositing material."

hydograph

"A graph showing the change in the amount of discharge over time. The shape of this graph reflects how a stream responds to precipitation, telling us useful information about a stream and the area it drains."

drainage basin

"A naturally defined area which each stream drains. They slope from higher areas where the stream begins, to lower areas, toward which the stream flows. Runoff from rainfall, snowmelt, and springs will flow downstream and out of the drainage basin at its lowest point."

closer

"CLOSER/FURTHER AWAY from *base level*, streams on the broad plain have a much *lower* gradient, and the surrounding landscape has less relief and appears relatively smooth. This plain has low relief because it has either been eroded down or its low parts have filled with sediment. In this case, it is some of both. "

Differential subsidence

"Can flatten or steepen gradients, depending on where it occurs."

Stream

"Carries flowing water through a single channel or through a number of interconnected channels. Such channels vary in szie from small streams to several meters wide to major rivers that are kilometers across."

Structurally Controlled Pattern

"Erosion along faults, joints or tilted and folded layers can produce a drainage that follows a layer or structure, and then cuts across a ridge to follow a different feature."

ultimate base level

"For most river systems, the *_ _ _* is sea level."

Tectonics

"Forces that can cause *uplift* or *subsidence* of an entire region or can occur differentially, affecting one part of the region more than other parts."

High above

"HIGH ABOVE/DOWN BELOW *base level*, steep gradients in the mountains cause streams to erode sharply into the bedrock. The terrain appears rough and may include deep canyons into bedrock."

Basin Slope

"Helps us determine how fast water in the basin empties after a heavy rain or after snowmelt."

lowered

"If base level RISES/ is LOWERED, such as by a _ in sea level, the stream will downcut to try to match the new base level."

equilibrium profile

"If conditions such as climate remain stable, a stream may approach an *_ _*."

rises

"If the base level RISES/ is LOWERED, such as during a _ in sea level, the stream will erode inland but will deposit sediment along the coastline's new position."

Foothills

"In front of the mountains, experience erosion but have intermediate gradients and generally appear less rough."

Basin Size and Shape

"Influence its flow response to rainfall."

Radial (drainage pattern)

"On a fairly symmetrical mountain, such as a volcano or resistant pluton, drainages flow downhill and outward in all directions away from the highest area."

The Potomac River

"River that winds its way along the MD and WV border n its way to D.C.. A number of smaller streams join the river from both sides, forming a river system. Water flowing in streams can move rock fragments and dissolved minerals from high elevations to low elevations.

Continental Divide

"Separating drainages that flow westward into the Pacific Ocean from those that flow westward into the Pacific Ocean from those that flow east and south into the Gulf of Mexico."

Dynamic systems

"Streams are *_ _* driven by precipitation and gravitational forces."

tributaries

"Streams have a main channel fed by smaller subsidiary channels called *_* Each drains part of the larger drainage basin, but it can have higher flows than a main stream." "The response of a stream to precipitation is influenced by the number and size of its _."

Climate

"Streams respond to changes in *_*, especially an increase or decrease in rainfall."

amount of water

"The _ _ _ that flows through a stream channel varies with time, mostly reflecting the influence of changes in the seasons (i.e. from winter to spring) and changes in the winter."

discharge (Q)

"The amount of water flowing in a given amount of time, which has units of cubic meters per second." stream depth x stream width x stream velocity

drainage network

"The combination of tributaries and the main stream." - smaller tributaries join to form larger drainages, which join to form even larger drainages. - The fewer tributaries, the more quickly a _ responds to an event.

base level

"The lowest level to which a stream can erode. This controls the topography along a stream, how a stream develops over time and how it responds to change." - ocean, lake or bottom of a closed land basin.

steep

"The profile is more STEEP/GENTLE near the headwaters of the stream."

drainage divide

"The ridge between the two drainage basins is the boundary between water flowing into different drainage basins."

Sea Level

"This is the ultimate base level for streams that empty into an ocean. Changes in this will change the location of the shoreline and the elevation of base level."

wet

"Under DRY/WET conditions, slopes will have more vegetation and so they can hold soil, but increase discharge allows streams to carry sediment away, beveling the hills more than during dry period."

irregular

"When a stream first forms during initial uplift of the land, the profile may be very *_*, especially if the stream crosses different rock types and geologic structures.

Dendritic (drainage pattern)

"Where rocks have about the same resistance to erosion, or if a drainage network has operated for a long time, streams form a treelike or *_* drainage pattern.

A

*What type of rock can help streams create a smooth, equilibrium like profile?* A) Unconsolidated sediment and easily eroded rocks, like shale. B) Alternating strong and weak rocks, rocks that are more resistant to erosion.

soft

Do HARD or SOFT rocks erode more easily than the other?

False (They generally do not reach equilibrium because some rocks are more difficult to erode than others and because Earth is a dynamic planet, with frequent changes in tectonics, sea level and climate.)

True or False: Streams generally reach equilibrium.

concave-up profile

What do the following qualities represent? 1) The profile is steeper (has a higher gradient) near the headwaters of the stream 2) In a downstream direction, the stream's profile becomes less steep (has a lower gradient). 3) Most rivers and large streams have this.

Rock Type, Tectonics, Sea Level, Climate, Stability of Conditions

What five factors influence or change stream profiles?

True

True or False: A stream CANNOT erode below sea level.