PHS 111 Test (Ch 5)

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

They form at or below the water table. The reverse reaction (of cave formation) occurs when water dripping into a cave evaporates and leaves behind a form of calcite called travertine, resulting in formations known as speleothems. They form above the water table. Some speleothems: stalactites - come down from ceiling (tite = hang tight from the ceiling) soda straws - hollow, water comes down inside til plugged and then comes down outside and stalactite gets fatter stalagmites - come up from ground (g = ground) columns - stalactites/stalagmites meet +many others

Book: In what direction do the meander loops of a meandering stream move?

They move laterally and downstream. Erosion is more effective going downstream.

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

They relate to a stream's transportation of sediment. 1. competence = maximum size particles transported, depends on the stream's velocity 2. capacity = maximum load transported, depends on stream's discharge -> both increase tremendously during floodstage, so much so that most of the erosion and transport of material occurs during floodstage

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?

"A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs)." When the drainage basin becomes urbanized, there is a shorter lag time and a higher peak of discharge. This leads to more flooding. After urbanization- fields and forests are replaced with impermeable surfaces (streets, parking lots, rooftops), more water runs off more quickly (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. After urbanization, more water runs off and less water soaks into the ground (water table lowered, dry season discharge decreased).

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

"In general, if base level is lowered, the stream cuts downward into its channel and erosion is accelerated. If base level is raised, the stream deposits sediment and readjusts its profile to the new base level."

List some characteristics of a karst topography.

-Caves -Disappearing/sinking streams -Springs (where water that has been underground comes out naturally at the surface) -Sinkholes -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

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

1. Dissolved load - most dissolved minerals come from ground water (ie evaporating sweet tea to leave sugar). 2. Suspended load - fin sand, silt, and clay particles in suspension. 3. Bed load - particles that are too heavy to be carried in suspension and that roll or bounce along the bottom (Colorado River in Grand Canyon - suspended load is responsible for muddy appearance).

Name and discuss the three types of "work" of streams.

1. Erosion: Mostly occurs during high-flow periods. Can be especially rapid if the bed and channel sides are composed of poorly consolidated material. Erosion typically dominates in the upstream area. If the stream has a bedrock channel, most of the erosion is by abrasion by its load of sediment. Gravel caught in swirling eddies can act like a drill and form potholes. 2. Transportation of sediment: Transports dissolved loads, suspended loads, and bed loads A stream's ability to transport sediment is determined by its competence and capacity, which both increase tremendously during floodstage, so much so that most of the erosion and transport of material occurs during floodstage. 3. Deposition: Occurs when the stream's velocity is reduced. Heavier particles settle out first resulting in sorting of the the material. All the sediment deposited by a stream is called alluvium. Channel deposits (tributary deposits sediment into other stream, other stream can't transport all) - mostly sand and gravel bars; braided streams can occur when the stream load > its ability. Deltas, floodplain deposits, and alluvial fans are also features related to deposition of sediment.

Name and describe factors that control stream velocity.

Ability of a stream to erode and transport its load of eroded material is strongly dependent on the velocity of its moving water. 1. Gradient (slope of stream channel): vertical drop per unit of horizontal flow; gradient of Mississippi River in LA is about 6 in/mi, a mountain stream may have a gradient > 200 ft/mi 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 (volume of water flowing past a point per second): discharge is width (ft) x depth (ft) x velocity (ft/sec); if the discharge increases, then the width or depth or velocity increases- usually all 3.

Distinguish between ultimate and temporary or local base level.

Base level = the lowest level to which a stream can erode its channel The base level can change up or down as a response to changed in the stream. A change in one characteristic will cause an adjustment in other characteristics of a stream. Ultimate base level = sea level Temporary/local base level = level where velocity/eroding power of water temporarily lost; a lake, a larger stream, a layer of resistant rock (anything other than the ocean that restricts the downward erosion of a stream). "Sea level is referred to as the ultimate base level, because all streams, rivers and waterways eventually erode toward that ultimate destination. But there is another type of base level that can be considered a temporary base level, because water gets stuck or stalled there for a period of time. This is called the local base level and we can define it as the level where the velocity and eroding power of the water is temporarily lost."

What are stream terraces and how are they formed?

They form after the base level of a floodplain is lowered and the river starts downcutting. "Stream terraces are deposits of old floodplain material oriented parallel to the river valley which forms an elevated area above a valley floor. These features develop when the base level of a previous floodplain is lowered and the river begins downcutting through the old floodplain material."

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

All the land that contributes water to a stream is called the stream drainage basin. A divide is what separates two drainage basins.

What term describes all the sediment deposited by a stream?

All the sediment deposited by a stream is called alluvium.

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

Caves form in limestone at or below the water table (limestone is very susceptible to attack by naturally acidic water). Carbonic acid is important to cave formation.

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; 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.

Name and recognize four stream drainage patterns.

Dendritic Pattern: controlled by slope of the land; develops on relatively uniform surface materials Radial Pattern: produced from domes or volcanoes; develops on isolated volcanic cones or domes Rectangular Pattern: controlled by underlying joints and faults; develops on highly jointed bedrock Trellis Pattern: occurs in areas of folded mountains; develops in areas of alternating weak and resistant bedrock

What are distributaries?

Distributaries = distribute water from main channel across delta

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

Equation: CO2 + H2O + CaCO3 -> Ca^2+ + 2HCO3 - Carbonic acid (H2CO3) + calcite -> limestone dissolved in water (when written as two elements as the solution to an equation, it indicates 2 separate items dissolved in water, can't be seen). "As rainwater comes through the soil it absorbs more carbon dioxide that is being produced by plants that are dead. This changes the ground water to a weaker form of carbonic acid(H2O + CO2 = H2CO3). As it travels down through the ground it comes to solid rock. When the rock is limestone or dolomite caves can form."

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

Example: A stream drops 110 ft over the course of it flowing 50 miles, what is the average gradient of the stream? Gradient - 110 ft/50 mi = 2.2 ft/mi

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

Headwaters-erosion is most important at this stage Middle section- transportation of sediment is most important at this stage Farthest downstream- deposition of sediment is most important at this stage

Thought question: If things happen in a meandering stream to cause the meanders to become entrenched or incised, the stream is often said to be "rejuvenated". Why do you think this term is used?

I think it is used because the stream now has characteristics of both youthful and old-age streams, whereas it was a fully developed old-age stream before. Now that it is showing youthful characteristics again in its advanced stage, it has been 'rejuvenated' or made young again.

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

In channel deposition, if the stream load is > its ability, then a braided stream results. Braided stream = when a 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 (ie downstream from a glacier).

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

Meanders form as faster-flowing water is forced to the outside bends of the river which is slightly meandering. On the inside of the banks, the water is less and slower, with more friction. On the outside, fast-flowing water is directed and causes more erosion. As this fast-moving current alternates with the bends in the river, the meanders widen. Point bars are formed by deposition of sediment, left by the slower-moving water of a river."A point bar is an area of deposition whereas a cut bank is an area of erosion. Point bars are formed as the secondary flow of the stream sweeps and rolls sand, gravel and small stones laterally across the floor of the stream and up the shallow sloping floor of the point bar." Oxbow lakes are formed as meanders grow so wide the land between the two sides becomes very close and the neck of land between the two sides bends. The land here gives way to allow the river to flow straight here again, cutting off the curve of the meander and leaving it as an isolated lake.

How is a natural bridge formed in a karst area?

Natural bridges are formed from the collapse of the roof of a cave tunnel.

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

Retention basins (ponds): they are partial remedies. They delay the entry of water into the stream runoff (increasing lag time and decreasing 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).

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

The Amazon River has the world's largest discharge, with 7,500,000 ft/sec. The Mississippi River ranks 8th, with the Congo being 2nd and Yangtze being 3rd.

What is an entrenched (incised) meander? What causes a rejuvenated stream to form?

The entrenched/incised meander is when a deep valley is formed and the meandering pattern becomes permanently embedded. If the base level of an old-age (meandering) stream drops or if the land is uplifted, down-cutting resumes and the meanders become entrenched/ incised. Deep, incised valleys with meanders result, and the stream takes on characteristics of both a youthful and old-age stream. It is now a rejuvenated stream. "As the stream erodes downwards, its established meandering pattern will remain as a deep valley known as an incised meander or entrenched meander. Rivers in the Colorado Plateau, the Kentucky River Palisades in central Kentucky, and streams in the Ozark Plateau are noted for these incised meanders."

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

The gradient decreases, the discharge increases (may decrease in arid regions), the width increases, the depth increases, the velocity increases (turbulent vs laminar flow- downstream less rocks/turbulence, more smooth/fast), sediment size decreases. Headwaters/head - origin of river Mouth - place river empties into another body of water

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

The idealized stages of valley development have nothing to do with the years involved to progress from one stage to another, they're merely a tool to classify stream characteristics. in an idealized sense they do represent the progression that will occur in the development of a stream valley. 1. Young Stream: shaped valley with steep valley walls; occur where the stream is well above its base level and the gradient is steep; has a narrow channel, the stream fills the valley floor, and there are no meanders The shape indicates that down-cutting is taking place faster than valley widening. Rapids and waterfalls result where the stream flows over more resistant rock layers which serve as a "temporary" base level for the stream. 2. Mature Stream: down-cutting has nearly stopped because the gradient is much less there are no rapids or waterfalls; a floodplain beings to develop as valley widening becomes the more dominant erosion; the stream begins to meander as it reworks the alluvium in its floodplain 3. Old Stream: it has a low gradient which results in a broad, flat floodplain; as the stream rewords its floodplain deposits, meandering becomes significant; the stream is usually not near its valley walls; meandering streams transport most of their load in suspension; deposition and re-erosion produce more rapid changes in the stream

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

These features are caused by floodplain deposits. Floodplain deposits - When a stream with a broad, flat floodplain overflows its banks, several features result (backswamp, yazoo tributary, natrual levee, etc). Yazoo tributary = flows roughly parallel to the main stream. When there is flooding in the river, these features are formed. During floods, the floodplain (flat land surrounding river) is inundated and largest particles of sediment are deposited at the walls of the channel where the normal boundaries of the river are, creating natural levees. When the water recedes to normal levels, sediment is deposited and backswamps form where fine silt and clay were deposited. Yazoo tributaries are formed by water left behind and forced to run parallel to the river after natural levees are formed.