Erosion The removal of rock material (weathered rock, boulders, gravel, sand, silt and clay) Erosion suggests transport, but transport is not necessarily.

Erosion The removal of rock material (weathered rock, boulders, gravel, sand, silt and clay) Erosion suggests transport, but transport is not necessarily erosion.

Transport Weathered rock and sediments and dissolved minerals are moved from the source area to the depositional area. Transport agents Running Water Wind Ice

Deposition Deposition occurs when the energy of the sediment transport agent decreases. Deposition occurs when the sediment can no longer be moved.

Lithification Lithification involves compaction and cementation that convert sediment into sedimentary rock. Silica and calcium carbonate are the most common chemical cements, but iron oxide and iron hydroxide cements are important in some rocks.

Rivers Rills to Rivers (channel flow) Sources:
sheet flow from rain and snow groundwater soil moisture Topographic High to Low (eventually to sea level—base level) Drainage Basin (all sheet flow and channel flow ends up in one major channel flow)

Figure 12.3: During the hydrologic cycle, water evaporates from the oceans and rises as water vapor to form clouds that release their precipitation over oceans or over land. Much of the precipitation falling on land returns to the oceans by surface runoff, completing the cycle. Water Cycle Fig. 12-3, p. 274

Rivers Rivers erode vertically and laterally
Rivers transport sediments and dissolved minerals Rivers deposit sediments

Hoover Dam and Lake Mead
Erosion or deposition? Figure 1a: Hoover Dam on the Colorado River in Nevada, where falling water generates electricity. The dam at 221 m high is the second highest in the United States. In addition to power generation, the reservoir functions in flood control, irrigation, and recreation. Figure 1a, p. 273

Note v-shaped valley shape
Erosion or deposition? Note steep gradient (much downcutting, cannot meander) Figure 12.1: The Yellowstone River looks small in this photo, but it has been responsible for carving what is called “The Grand Canyon of the Yellowstone” in Yellowstone National Park, Wyoming. Fig. 12-1, p. 270

What happens when Niagara slips?
Horseshoe Falls The Niagara River spills over Niagara Falls near the border between Canada and the United States. Note the volume of mist moving upward from the base of the falls. Niagara Falls! Fig. 12-CO, p. 268

How do rivers erode? Cutting power of rivers is recognized over time and during periods of excessive flow (e.g., flood stage) Steeper gradients increase downcutting Shallow gradients decrease downcutting but increase lateral flow.

Stream Gradient head Rapid stream velocity, bed load is coarse, erosion is downward. Slow stream velocity, bed load is fine, erosion is lateral, stream meanders Figure 12.4: The average gradient of this stream is 2 m/km, but gradient can be calculated for any segment of a stream, as shown in this example. Notice that the gradient is steepest in the headwaters area and decreases in a downstream direction. mouth Fig. 12-4, p. 274

Figure 12.5: Flow velocity in rivers and streams varies as a result of friction with their banks and beds. (b) These three differently shaped channels have the same cross-sectional area. But the semicircular one has less water in contact with its perimeter and thus less frictional resistance to flow. Fig. 12-5b, p. 275

Stream Features Load Primary and Secondary Channel Flood Plain
Sediment load (boulders, gravel, sand), also called bed load Suspended load (silt and clay) high energy events can carry sand and gravel Dissolved load (dissolved minerals) Primary and Secondary Channel Flood Plain Cut Bank vs. Point Bar Meanders and Ox-Bow Lakes Delta Alluvial Fan (intermittent stream)

Stream Load

Braided Stream, New Zealand
Can be caused by additional influx of sediments or a change in topography causing a lowering of the stream gradient Figure 12.7: Braided streams and their deposits. (a) A braided stream as seen from the air in New Zealand. Fig. 12-7a, p. 278

Braided stream, Chester, California
Figure 12.7: Braided streams and their deposits. (b) A braided stream with gravels bars near Chester, California. Braided stream, Chester, California Fig. 12-7a, p. 278

Primary and Secondary Channels of a Stream
Primary Channel Secondary Channel Figure 12.11: (a) Floodplain deposits form as a meandering stream migrates laterally, depositing a series of point bars. (b–d) Three stages in the formation of deposits on a floodplain. (b) Stream at low-water stage. (c) Flooding stream and deposition of natural levees. The levees form after many such episodes of flooding. (d) After flooding. Notice the tributary stream, which parallels the main stream until it finds a way through the natural levee. During a flood, the secondary channel begins to fill Fig , p. 281

Figure 12. 12a: This small stream runs parallel to a downtown area
Figure 12.12a: This small stream runs parallel to a downtown area. The photo was taken on a typical summer day. Note the building and railing on the left for comparison with the next photo. Fig a, p. 281

Figure 12.12b: This photo was taken from the same spot in the late winter. Compare the buildings to see that the photos are a matched pair. Note the near-flood-stage state of the stream. On the left edge you can see sandbags that downtown merchants prepared to keep water in the stream channel. Fig b, p. 281

Figure 12.11: (b–d) Three stages in the formation of deposits on a floodplain. (b) Stream at low-water stage. Fig b, p. 281

Figure 12.11: (b–d) Three stages in the formation of deposits on a floodplain. (c) Flooding stream and deposition of natural levees. The levees form after many such episodes of flooding. Fig c, p. 281

Figure 12.11: (b–d) Three stages in the formation of deposits on a floodplain. (d) After flooding. Notice the tributary stream, which parallels the main stream until it finds a way through the natural levee. Fig d, p. 281

Figure 12.9: (a) In a meandering channel, flow velocity is greatest near the outer bank. The dashed line follows the path of maximum velocity, and the lengths of the solid arrows are proportional to velocity. Because of varying velocity across the channel, the outer bank or cut bank is eroded but a point bar is deposited on the opposite side of the channel. (b) Two small point bars of sand in a meandering stream. Notice how they are inclined into the deeper part of the channel. Also note the cut bank. (c) The Colorado River in Canyonlands National Park, Utah, has a cut bank (left bank) and a point bar (right bank) covered with vegetation. Also note the color of the stream, which indicates that it contains a large volume of suspended sediment. Fig. 12-9, p. 279

Figure 12.9a: In a meandering channel, flow velocity is greatest near the outer bank. The dashed line follows the path of maximum velocity, and the lengths of the solid arrows are proportional to velocity. Because of varying velocity across the channel, the outer bank or cut bank is eroded but a point bar is deposited on the opposite side of the channel. Fig. 12-9a, p. 279

Figure 12. 9b: Two small point bars of sand in a meandering stream
Figure 12.9b: Two small point bars of sand in a meandering stream. Notice how they are inclined into the deeper part of the channel. Also note the cut bank. Fig. 12-9b, p. 279

Sediment load added by erosion at the river bank
Cut Bank Figure 12.6: (a) This stream acquires some of its sediment load by undercutting its banks, whereas in (b) mass wasting supplies sediment to this stream. Sediment load added by erosion at the river bank Fig. 12-6a, p. 277

Figure 12.9c: The Colorado River in Canyonlands National Park, Utah, has a cut bank (left bank) and a point bar (right bank) covered with vegetation. Also note the color of the stream, which indicates that it contains a large volume of suspended sediment. Fig. 12-9c, p. 279

Cut Bank Point Bar Crossbedding Fig. 12-11a, p. 281
Figure 12.11: (a) Floodplain deposits form as a meandering stream migrates laterally, depositing a series of point bars. Crossbedding Fig a, p. 281

Meandering Stream, low stream gradient, Laxa River, Iceland
Figure 12.8: The Laxa River in Iceland has many meanders. In the middle of the photo is a meander so extreme the stream will likely soon “cut off” the meander and begin the formation of an oxbow lake. Note preliminary formation of an ox-bow lake Fig. 12-8, p. 278

Active Figure 12. 10: Four stages in the origin of an oxbow lake
Active Figure 12.10: Four stages in the origin of an oxbow lake. In (a) and (b), the meander neck becomes narrower. (c) The meander neck is cut off, and part of the channel is abandoned. (d) When it is completely isolated from the main channel, the abandoned meander is an oxbow lake. Fig , p. 280

Active Figure 12.10: Four stages in the origin of an oxbow lake. In (a) and (b), the meander neck becomes narrower. Fig a, p. 280

Active Figure 12.10: Four stages in the origin of an oxbow lake. In (a) and (b), the meander neck becomes narrower. Fig b, p. 280

Active Figure 12.10: Four stages in the origin of an oxbow lake. (c) The meander neck is cut off, and part of the channel is abandoned. Fig c, p. 280

Active Figure 12.10: Four stages in the origin of an oxbow lake. (d) When it is completely isolated from the main channel, the abandoned meander is an oxbow lake. Fig d, p. 280

Incised meanders—area must have undergone some uplift
Figure 12.23: The deeply entrenched meanders of the San Juan River in Utah cut through many layers of sedimentary rock. The dramatic meanders are informally known as “goosenecks” because they loop so sharply back on themselves. The San Juan River cannot erode laterally because it is effectively restricted by the 400-m rock walls around it, so it has no floodplain but simply occupies the whole base of the canyon. Incised meanders—area must have undergone some uplift Fig , p. 291

Velocity of the stream is reduced at the mouth of the river.
Delta Figure 12.13a: Internal structure of the simplest type of prograding delta. Velocity of the stream is reduced at the mouth of the river. The sediment and suspended load begins to settle out Sorting: coarser grains nearer the mouth, finer grains further away Fig a, p. 282

Delta Deposition Pattern
Topset Beds Foreset Beds Figure 12.13b: A small delta, measuring about 20 m across, in which bottomset, foreset, and topset beds are visible. Bottomset Beds Delta Deposition Pattern Fig b, p. 282

Mississippi River Delta— birds foot delta
Figure 12.13c: The Mississippi River delta of the U. S. Gulf Coast. Fig c, p. 282

Alluvial Fans (much coarser-grained than deltas)
Form when heavy rainstorms occur in sparsely-vegetated semi-arid regions. Figure 12.14: (a) Alluvial fans form where streams discharge from mountain canyons onto adjacent lowlands. (b) Alluvial fans adjacent to the Panamint Range on the margin of Death Valley, California. Fig , p. 283

Figure 12.14a: Alluvial fans form where streams discharge from mountain canyons onto adjacent lowlands. Fig a, p. 283

Figure 12.14b: Alluvial fans adjacent to the Panamint Range on the margin of Death Valley, California. Fig b, p. 283

Idealized Stages in the Development of a Stream.
Figure 12.21: Idealized stages in the development of a stream and its associated landforms. Fig , p. 290

Younger, steeper gradient Downcutting erosion
Figure 12.21: Idealized stages in the development of a stream and its associated landforms. Fig a, p. 290

Intermediate gradient
Figure 12.21: Idealized stages in the development of a stream and its associated landforms. Fig b, p. 290

Low gradient, mature stream approaching base level
Figure 12.21: Idealized stages in the development of a stream and its associated landforms. Fig c, p. 290

Eventually, downcutting will lead to the formation of terraces (which are erosional remnants of floodplains. Figure 12.22: Origin of stream terraces. (a) A stream has a broad floodplain. (b) The stream erodes downward and establishes a new floodplain at a lower level. Remnants of its old, higher floodplain are stream terraces. (c) Another level of stream terraces forms as the stream erodes downward again. (d) Stream terraces along the Madison River in Montana. Fig , p. 291

Figure 12. 22: Origin of stream terraces
Figure 12.22: Origin of stream terraces. (a) A stream has a broad floodplain. Fig a, p. 291

Figure 12.22: Origin of stream terraces. (b) The stream erodes downward and establishes a new floodplain at a lower level. Remnants of its old, higher floodplain are stream terraces. Fig b, p. 291

Figure 12.22: Origin of stream terraces. (c) Another level of stream terraces forms as the stream erodes downward again. Fig c, p. 291

Figure 12.22: Origin of stream terraces. (d) Stream terraces along the Madison River in Montana. Fig d, p. 291

Drainage Basin Figure 12.15: (a) Small drainage basins separated by divides (dashed lines) are along the crests of the ridges between channels (solid lines). (b) The drainage basin of the Wabash River, which is one of the tributaries of the Ohio River. All tributary streams within the drainage basin, such as the Vermillion River, have their own smaller drainage basins. Divides are shown by dark red lines. Fig , p. 285

Small scale drainage basins follow topography
Divide Figure 12.15a: Small drainage basins separated by divides (dashed lines) are along the crests of the ridges between channels (solid lines). Small scale drainage basins follow topography Fig a, p. 285

Wabash River Drainage Basin
Figure 12.15b: The drainage basin of the Wabash River, which is one of the tributaries of the Ohio River. All tributary streams within the drainage basin, such as the Vermillion River, have their own smaller drainage basins. Divides are shown by dark red lines. Fig b, p. 285

Stream Drainage Patterns
Figure 12.16: Examples of drainage patterns. (a) Dendritic drainage. (b) Rectangular drainage. (c) Trellis drainage. (d) Radial drainage. (e) Deranged drainage. Stream Drainage Patterns Fig , p. 286

Dendritic Figure 12.16: Examples of drainage patterns. (a) Dendritic drainage. Fig a, p. 286

Rectangular—controlled by solution joints
Figure 12.16: Examples of drainage patterns. (b) Rectangular drainage. Fig b, p. 286

Trellis Figure 12.16: Examples of drainage patterns. (c) Trellis drainage. Fig c, p. 286

Radial Figure 12.16: Examples of drainage patterns. (d) Radial drainage. Fig d, p. 286

Deranged—swampy regions
Figure 12.16: Examples of drainage patterns. (e) Deranged drainage. Fig e, p. 286

Figure 12.17: (a) Sea level is ultimate base level, and a resistant rock layer forms a local base level. (b) Cumberland Falls on the Cumberland River in Cumberland Falls State Resort Park, Kentucky. The rock layer the falls plunge over is a local base level. At 38 m wide and 18 m high, Cumberland Falls is the second highest waterfall east of the Rocky Mountains. (c) Small but dramatic cataracts like Multnomah Falls in the Columbia River Gorge between Oregon and Washington create a local base level at their top, clearly distinct from lower base levels down-valley. There is a series of similar falls in the Columbia River Gorge, all of which were created when enormous Ice Age floods moving down the Columbia deepened and widened the gorge. Fig , p. 288

Figure 12.17a: Sea level is ultimate base level, and a resistant rock layer forms a local base level. Fig a, p. 288

Figure 12.17b: Cumberland Falls on the Cumberland River in Cumberland Falls State Resort Park, Kentucky. The rock layer the falls plunge over is a local base level. At 38 m wide and 18 m high, Cumberland Falls is the second highest waterfall east of the Rocky Mountains. Fig b, p. 288

Figure 12.17c: Small but dramatic cataracts like Multnomah Falls in the Columbia River Gorge between Oregon and Washington create a local base level at their top, clearly distinct from lower base levels down-valley. There is a series of similar falls in the Columbia River Gorge, all of which were created when enormous Ice Age floods moving down the Columbia deepened and widened the gorge. Fig c, p. 288

Figure 12.18: (a) The process of constructing a dam and impounding a reservoir creates a local base level. A stream deposits much of its sediment load where it flows into a reservoir. (b) A stream adjusts to a lower base level when a lake is drained. Fig , p. 289

Figure 12.18a: The process of constructing a dam and impounding a reservoir creates a local base level. A stream deposits much of its sediment load where it flows into a reservoir. Fig a, p. 289

Figure 12.18b: A stream adjusts to a lower base level when a lake is drained.
Fig b, p. 289

Figure 12.19: (a) An ungraded stream has irregularities in its longitudinal profile. (b) Erosion and deposition along the course of a stream eliminate irregularities and cause it to develop the smooth, concave profile typical of a graded stream. Fig , p. 289

Figure 12.19a: An ungraded stream has irregularities in its longitudinal profile.
Fig a, p. 289

Figure 12.19b: Erosion and deposition along the course of a stream eliminate irregularities and cause it to develop the smooth, concave profile typical of a graded stream. Fig b, p. 289

Arrgh! Headward erosion in a valley and stream piracy.
Figure 12.20: Two stages in the evolution of a valley. (a) The stream widens its valley by lateral erosion and mass wasting, while simultaneously extending its valley by headward erosion. (b) As the larger stream continues to erode headward, stream piracy captures some of the drainage of the smaller stream. Notice also that the larger valley is wider in (b) than it was in (a). Arrgh! Fig , p. 289

Figure 12. 20: Two stages in the evolution of a valley
Figure 12.20: Two stages in the evolution of a valley. (a) The stream widens its valley by lateral erosion and mass wasting, while simultaneously extending its valley by headward erosion. Fig a, p. 289

Figure 12. 20: Two stages in the evolution of a valley
Figure 12.20: Two stages in the evolution of a valley. (b) As the larger stream continues to erode headward, stream piracy captures some of the drainage of the smaller stream. Notice also that the larger valley is wider in (b) than it was in (a). Fig b, p. 289

CHAPTER OUTLINE Introduction The Hydrologic Cycle Running Water GEO-FOCUS 12.1: Dams, Reservoirs, and Hydroelectric Power How Running Water Erodes and Transports Sediment Deposition by Running Water Drainage Basins and Drainage Patterns CULTURAL CONNECTIONS: Flood Stories from Around the World Base Level Graded Streams Valley Evolution Geo-Recap

CHAPTER OBJECTIVES 1 Running water, one part of the hydrologic cycle, does considerable geologic work. Water is continuously cycled from the oceans to land and back to the oceans. 2 Gradient measures how steep a stream is. Discharge measures the volume of water that passes a given point per unit of time. Discharge, along with velocity, usually increases downstream. 3 Running water transports large quantities of sediment and deposits sediment in or adjacent to braided and meandering rivers. 4 Flooding is a natural part of stream activity that takes place when a channel receives more water than it can handle. 5 Alluvial fans (on land) and deltas (in a standing body of water) are deposited when a stream’s capacity to transport sediment decreases. 6 Rivers and streams continuously adjust to changes. Base level is the elevation below which a stream cannot erode. Waterfalls and lakes are temporary base levels, and the sea is ultimate base level.

CHAPTER OBJECTIVES 7 The concept of a graded stream is an ideal, although many rivers and streams approach the graded condition. 8 Most valleys form and change in response to erosion by running water coupled with other geologic processes such as mass wasting.

Available Fresh Water Fig. 12-2, p. 270
Figure 12.2: The relative amounts of water on Earth. Of the estimated 1.36 billion km3 of water, 97.2% is in the oceans; most of the rest, 2.15%, is frozen in glaciers on land. Available Fresh Water Fig. 12-2, p. 270

Figure 12.5: Flow velocity in rivers and streams varies as a result of friction with their banks and beds. (a) The maximum flow velocity is near the center and top of a straight channel where friction is least. The arrows are proportional to velocity. (b) These three differently shaped channels have the same cross-sectional area. But the semicircular one has less water in contact with its perimeter and thus less frictional resistance to flow. Fig. 12-5, p. 275

Figure 1b: At hydroelectric dams water rushes through the penstock and spins a turbine connected by a shaft to an electromagnet within a generator. The spinning electromagnet inside a coil of wire generates electricity. Figure 1b, p. 273

Figure 12.5: Flow velocity in rivers and streams varies as a result of friction with their banks and beds. (a) The maximum flow velocity is near the center and top of a straight channel where friction is least. The arrows are proportional to velocity. Fig. 12-5a, p. 275

CHAPTER SUMMARY Water continuously evaporates from the oceans, rises as water vapor, condenses, and falls as precipitation. About 20% of all precipitation falls on land and eventually returns to the oceans, mostly by surface runoff. A channel’s gradient varies from steep in its upper reaches to gentle in its lower reaches. Flow velocity and discharge are related, so a change in one results in a change in the other. Velocity and discharge increase downstream in most rivers and streams. Running water erodes by hydraulic action, abrasion, and dissolution of soluble rocks. The larger particles transported by running water move as bed load, whereas the smallest particles move as suspended load. Rivers and streams also transport a dissolved load of materials in solution. Braided streams have complex, multiple, intertwining channels. Their deposits consist mostly of sand and gravel.

CHAPTER SUMMARY Meandering streams have a single, sinuous channel in which point bars of sand or gravel are deposited. Cutoff meanders known as oxbow lakes eventually fill with fine-grained sediments and organic matter. Floodplain deposits might consist of a succession of point bars deposited by a migrating channel, or mud deposited by water carried into the floodplain during floods. Deltas form where a river or stream enters a standing body of water and deposits its sediment load. Small deltas in lakes commonly have a three-part division of bottomset, foreset, and topset beds, but marine deltas are larger, more complex, and more important economically. In arid and semiarid regions where a river or stream flows from a mountain canyon onto adjacent lowlands, a deposit known as an alluvial fan accumulates. Alluvial fans consist of stream-deposited sand and gravel and/or mudflow deposits. Rivers and streams along with their tributaries carry runoff from areas known as drainage basins, which are separated by divides.

CHAPTER SUMMARY Sea level is ultimate base level, the lowest level to which rivers and streams can erode. Local or temporary base levels are lakes, other rivers or streams, or particularly resistant rocks. Rivers and streams tend to eliminate irregularities in their channels so that they develop a smooth, concave profile of equilibrium. These so-called graded streams approach this ideal condition only temporarily. Valleys develop and evolve by several processes, including downcutting, lateral erosion, headward erosion, stream piracy, and mass wasting. The formation of a floodplain, followed by renewed downcutting by a stream, leaves remnants of the older floodplain at higher levels known as stream terraces.

Sediment added to stream by mechanical weathering and erosion
Mass wasting Figure 12.6: (a) This stream acquires some of its sediment load by undercutting its banks, whereas in (b) mass wasting supplies sediment to this stream. Sediment added to stream by mechanical weathering and erosion Fig. 12-6b, p. 277

Figure 12.6: (c) A pothole near the edge of a stream in upstate New York.
Pothole formed by cutting power of falling water and abrasion from rock inside the pothole. Fig. 12-6c, p. 277

Note roundness of the boulders inside the pothole.
Figure 12.6: (d) Close-up view of a dry, 2-m-diameter pothole in Lucerne, Switzerland. Notice the large boulders in the pothole. Note roundness of the boulders inside the pothole. Fig. 12-6d, p. 277

Stream Deposits Levee Flood plain deposits
Braided streams (sediment load is greater than velocity can move) Deltas (velocity decreases as stream enters larger body of water-not channel flow, allowing for deposition) Alluvial fans (“semiarid delta”)

Stream Gradient Slope of the channel as it flows downhill.
Steeper gradient in upper reaches, near headwaters, Stream gradient gets progressively smaller towards base level. Steep gradient streams are generally straight and cut downward. Shallow gradient streams meander and generally cut sideways (laterally).

Erosion The removal of rock material (weathered rock, boulders, gravel, sand, silt and clay) Erosion suggests transport, but transport is not necessarily.

Similar presentations

Presentation on theme: "Erosion The removal of rock material (weathered rock, boulders, gravel, sand, silt and clay) Erosion suggests transport, but transport is not necessarily."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Erosion The removal of rock material (weathered rock, boulders, gravel, sand, silt and clay) Erosion suggests transport, but transport is not necessarily.

Similar presentations

Presentation on theme: "Erosion The removal of rock material (weathered rock, boulders, gravel, sand, silt and clay) Erosion suggests transport, but transport is not necessarily."— Presentation transcript:

Similar presentations

About project

Feedback