Question 1

The deepest part of a curved stream channel,where the flow is fastest,is called the ________.

Accepted Answer

The thalweg is the line of lowest points in a stream channel where the water flows the fastest. Option A is incorrect because base level refers to the lowest point to which a stream can erode its bed, not necessarily where the flow is fastest. Option B refers to a deposit of sediment found on the inside of a meander bend, and option C refers to the steepness or slope of a stream channel.

Question 2

A "bird's foot" delta such as the Mississippi River delta forms when the ________.

Accepted Answer

A "bird's foot" delta forms when the river current exceeds the oceanic current, allowing sediment to be deposited and build up over time.

Question 3

The distinction between a valley and a canyon is ________.

Accepted Answer

Canyons typically have more vertical and steep sides than valleys, which tend to have more gradual slopes. The formation processes can also differ, with canyons often formed by erosion from a river or water source, while valleys can be formed by a variety of processes including glacial activity, tectonic movement, or erosion.

Question 4

The average velocity of water in a stream

Accepted Answer

The average velocity of water in a stream is an approximation that accounts for friction and turbulence. It is not simply the velocity at the surface of the stream or in the inside of curves in the stream's path. It is also not the velocity at which all of the water is moving, as there may be variation in velocity throughout different parts of the stream.

Question 5

What physical property of the underlying rock would lead to the formation of a cliff over which a waterfall may form?

Accepted Answer

A high resistance to erosion would lead to the formation of a cliff over which a waterfall may form, as the water will erode the softer and less resistant rock around it, leaving behind the more resistant rock as a cliff.

Question 6

Repeated flooding outside a stream channel and across an entire floodplain can result in a pair of low ridges on either side of a stream termed

Accepted Answer

These low ridges are known as natural levees and form due to repeated flooding outside the stream channel on the floodplain. Cut banks are steep banks formed by erosion from the stream channel, pirated streams are streams that divert flow from another stream, and oxbow lakes are formed when a meander is cut off from the main channel. None of these options describe the formation of low ridges on either side of a stream.

Question 7

If over time a stream experiences a decrease in its base level or increase in discharge,a(n)________ is likely to form.

Accepted Answer

A decrease in base level or an increase in discharge can lead to the formation of alluvial terraces as the stream cuts down into its bed, leaving step-like landforms.

Question 8

The base level of a tributary would ________ if a dam and a reservoir were constructed where it flowed into a trunk stream.

Accepted Answer

If a dam and a reservoir were constructed where a tributary flows into a trunk stream, the water level would rise due to the blocked passage of water. The water level in the reservoir would be higher than the elevation of the tributary's base level, causing water to back up into the tributary and increase its water level.

Question 9

In some cases,the push of flowing water cause large particles to bounce or roll along a streambed.These pieces are then carried along the bottom of the stream as _________.

Accepted Answer

The large particles that bounce or roll along the streambed are part of the bed load, which is the portion of a stream's sediment load that is made up of particles that travel on, or immediately above, the streambed. The suspended load consists of smaller particles that are carried by the water and stay in suspension in the water column, while the dissolved load consists of dissolved minerals and chemicals that are carried by the water. Discharge refers to the amount of water flowing in a stream.

Question 10

A geologist finds an old report on stream discharge and reads a value of "20",but the rest of the page is cut off.Which of the following could be the appropriate value and units for the discharge of a stream?

Accepted Answer

Stream discharge is typically measured in cubic meters per second, which represents the volume of water flowing past a given point in the stream in one second. Choice A (meters per second) would represent the velocity of the water, not the volume. Choice C (square meters per second) does not make sense as it implies a measure of area instead of volume. Choice D (seconds per cubic meter) also does not make sense as it does not represent a meaningful measure of stream discharge.

Question 11

Meandering streams ________.

Accepted Answer

Meandering streams have a channel that is highly sinuous or curvy. Option A describes braided streams, option B describes intermittent streams, and option D describes a stream diversion.

Question 12

Which of the following is most likely to make up the suspended load of a stream?

Accepted Answer

The suspended load of a stream is made up of small grains of clay and silt that remain suspended in the water column and give the water its turbidity. Option A is incorrect because dissolved ions would not be part of the suspended load, but instead would be part of the dissolved load. Option B is incorrect because large boulders would be too heavy to remain suspended in the water column and would instead be part of the bed load. Option C is also incorrect because while gravel may be part of the bed load, it is typically too heavy to remain suspended in the water column as part of the suspended load.

Question 13

The discharge of a river traveling through a temperate region will typically ________ downstream; the discharge of a river traveling through an arid region will typically ________ downstream.

Accepted Answer

The answer of The discharge of a river traveling through...

Question 14

Why do deltas form?

Accepted Answer

Deltas form when streams reach their base level (typically the sea) and the sediment they carry settles out and is deposited. This process is known as sedimentation and is what creates the characteristic fan shape of a delta.

Question 15

The shape of a delta is primarily determined by ________.

Accepted Answer

The shape of a delta is primarily determined by whether river currents or ocean currents are locally predominant, as these currents influence the distribution and deposition of sediments at the river's mouth.

Question 16

What shape does the longitudinal profile of a typical stream follow? A longitudinal profile plots elevation of a streambed with distance,showing the streambed elevation from its highest point upstream to the lowest point at base level.

Accepted Answer

The longitudinal profile of a typical stream follows a concave upward shape, meaning that it starts at a higher elevation at the source and gradually decreases in elevation as it flows downstream towards the base level. This is due to erosion and deposition processes along the stream channel, which result in a steeper gradient near the source and a more gentle gradient near the base level. A straight diagonal line or horizontal line would suggest a uniform gradient, which is not typically the case for a naturally flowing stream. A line with random high and low points would not provide a coherent representation of the stream profile.

Question 17

Ultimately,the base level of a stream valley cannot be lower than ________.

Accepted Answer

The base level of a stream valley represents the lowest point to which a stream can erode its channel. Sea level is the ultimate base level beyond which a stream cannot erode its channel any further, so the base level of a stream valley cannot be lower than sea level.

Question 18

The flat-lying area surrounding a river channel is termed the ________.

Accepted Answer

The flat-lying area surrounding a river channel is referred to as the floodplain. Base level refers to the lowest point to which a stream can erode its channel, stream gradient is the steepness of the slope of a stream, and thalweg refers to the deepest point in a stream channel.

Question 19

Braided streams ________.

Accepted Answer

Braided streams consist of a series of intertwined channels that are overloaded with sediment. This sediment overload causes the stream to divide into multiple channels, creating a braided appearance.

Question 20

In the picture below,fragments of bed load bounce along the bed and knock other grains up into the flow to move downstream for short distances.This process is called

Accepted Answer

The bouncing process of bed load fragments is known as saltation.

Quiz 14: Streams and Floods: the Geology of Running Water