1. Floodplain Management SESSION 2
Stream Systems on
Dynamic Earth
Geologic Framework
Prepared By
Donald R. Reichmuth, PhD.
Title Page for Session 2

2. Geologic Framework Objectives: Define Floodplains
Describe Stream System Functions
Explain Tectonic Plates
Explain Vertical Plate Motion
Identify Tectonic Domains
Summarize Glacial Behavior
Compare Erosion Related Processes
Slide PP2.0-1 This slide lays out the objectives to be presented in this session. The instructor should be tell the students what they are going to hear; then present the information and finally tell them what was said.

3. River Basin Definition
A region or area
bounded by a topographic divide
that contributes water
to a particular stream channel (corridor)
or other water body.
Slide PP The session is started by defining a river basin. It should be made clear that this term is preferred over “watershed” because watershed has a dual meaning that can cause confusion.

4. Floodplain Definition
Slide PP This slide shows that transported sediment can be found on Active and Inactive Stream Terraces; on Alluvial Fans; on Bedrock Canyon Floors and as Buried Fill covering valley floors. Note that Transported Sediment needs to be differentiated from Residual Soil that forms in place when bedrock disintegrates. Diagram used by permission of Geomax, P.C., Spokane, WA
That portion of a Drainage Basin
that is covered by Transported Sediment
that was deposited in or near a stream channel.

5. FUCTIONS OF RIVER SYSTEMS
Removes Erosional Debris
Most Important
Acts Over Long Periods
Removes Excess Water
Importance Secondary
Acts Sporadically Over Short Periods
Provides Fresh Water Supply
Necessary To Sustain Life
Transports Chemicals & Nutrients
Slide It is extremely important to stress that a River System involves more than water. The four primary functions cannot be separated and problems associated with the removal of erosional debris usually cause the largest instabilities in river basins.

6. Geologic Framework Tectonics Glaciation Geomorphology Passive Margins
Stable Platforms
Active Margins
Hot Spots
Glaciation
Alpine Glaciers
Continental Glaciers
Geomorphology
Surface Forming Processes
Water
Ice
Gravity
Wind
Slide PP There are three branches of geology that must be understood if floodplain management is to successfully solve site specific problems. The earth’s dynamics, often not appreciated by the lay public because the processes are often slow and subtle, determine how the earth’s surface is sculptured.

7. Present Plate Boundaries
Slide PP This slide shows the locations and sizes of the seven continental-sized and eight minor plates of the earth’s surface. It is important to explain: 1) North America separated from Eurasian and African plates about 200 million years ago. 2) North American and South American plates have only had a surface connection for the last 2 million years and 3) Western Siberia is part of the North American Plate. Taken from Kious & Tilling, 1996, USGS

8. BASIC TYPES OF PLATE INTERACTION
Stream Systems on
Dynamic Earth
Slide PP This slide depicts an idealized cross-section through the earth that shows various conditions that affect tectonic plates. Included are Convergent, Transform and Divergent Plate Boundaries. Additionally, hot spots, volcanoes, trenches and rifts zones are shown.
Taken from Kious & Tilling, 1996, USGS

9. North America Structure Tectonic Activity Craton Mobile Belts
Shield
Stable Platform
Mobile Belts
Tectonic Activity
Active Margin
Passive Margin
Slide PP This slide shows the location of the major structural units that form North America. These units consist of the Craton that includes the Sheild and Stable Platform and the surrounding Mobile Belt. Because the North American Plate is moving westward, the West Coast is an Active Margin while the East Coast is a Passive Margin. It is important to note that the Stable Platform contains considerable limestone that formed in warm shallow seas when the area was much nearer to the equator. Base Adapted from Dott and Batten, 1971

10. Karst Topography Example
Slide PP This slide is an example of topography that forms on limestone. In humid climates, organic acids attack limestone creating solution cavities. These cavities often capture surface drainage creating sinkholes, Uvalas, and blind valleys. These surfaces are called Karst Topography. When limestone migrates (by tectonic plate movement) into dryer, colder climates further attack by organic acid significantly slows and limestone becomes one of the stronger rock formations. Adapted from a William J. Wayne Drawing
Solution Cavities In Limestone
Streams Have Subsurface Connections

11. Cretaceous Inland Sea 100 Million Years Ago
Slide PP This slide depicts surface conditions that existed in the U.S. during the Cretaceous Period 100 million years ago. There were the old worn down Appalachian Mtns. in northeastern U.S. and young high mountains in the Rocky Mtn. region. Between these two land masses was a Shallow Sea that cover the Central Plains and the Gulf Coast. Large shale deposits formed in the shallow sea. These shale deposits are now on the surface and are easily eroded.

12. Vertical Plate Motion Causes: Tectonic/Earthquake Activity
Erosion & Sediment Loading
Glaciation
Human Activities
Slide PP The earth’s surface is constantly moving. Vertical shifts can alter stream gradients and change erosion rates.

13. Uplift Example
Slide PP This slide shows the movement and collision of the Indian Plate. The Indian Plate rammed into the Eurasian Plate about 10 million years ago. Because both plates consist of lighter granitic rock (continental crust) neither would subduct, therefore the collision zone thickened forming the Himalayan Mtns. This collision provides an excellent model of uplift and erosion because the relative plate motion is about the highest seen; the mountains have been uplifted to be the tallest mountains that currently exist and sediment concentration in the area’s rivers is the highest known.
Taken from Kious & Tilling, 1996, USGS

14. Himalayan Data Present Height --- Tectonic Uplift Rate ---
30,000 Ft (9,500 m)
Tectonic Uplift Rate ---
More Than 1 cm/yr
Erosion Rate ---
Now Equals Uplift Rate
Sediment Yields Highest Known
Slide PP This slide provides the basic data to illustrate the end point when tectonic uplift equals erosion rate. This balance is achieved because erosion increases dramatically as surface elevation increases.

15. Worldwide Erosion Rates
Slide PP This slide shows the Denudation Rates for many of the earth’s major river basins. Note: Rates are Basin Wide Averages. The highest rates (500 mm/1000yrs) are concentrated around the Himalaya Mtns. and in eastern China. Africa and Siberia have some of the lowest erosion rates (10 to 25 mm/1000 years). North America has rates that range between 10 and 100 mm/1000 years. The Colorado River Basin has the highest rate in North America.
Adapted from Skinner & Porter, 2000

16. Oceanic-Continental Convergence
Oceanic Crust Subducts
Ocean Trench Forms
Lighter Melted Material Rises
Volcanoes Form
Lithosphere Plunges Into Asthenosphere
Slide PP This slide shows how an Oceanic Plate subducts under a Continental Plate and causes Volcanoes to form as lighter Lithospheric material melts and raises through the Continental Crust. Additionally, the downward bending Oceanic Plate causes a Trench to form along the Continental coast.
Taken from Kious & Tilling, 1996, USGS

17. Effects Of Plate Locking
Slide PP This slide depicts the vertical ground movements that occur a subducting Oceanic Plate locks to a Continental Plate as they converge. A buckle forms when the Trench is dragged downward. The buckle can raise 2 to 4 mm/year, while further inland the Plate sinks. When the lock is broken during an Earthquake, the Continental Plate snaps back to its unstrained (unbuckled) position causing Continental Plate to move vertically back to it unstrained position.
Adapted from Geological Survey of Canada, Pacific Geoscience Center diagram.

18. Effects Of Erosion
Slide PP This slide illustrates how isostatic equilibrium is maintained when mountains are eroded away. Mountains have roots of lighter rock extending into the Asthenosphere that provide buoyancy for the uplifted mass. As the mountain surface is eroded away, the entire mountain rises making the root smaller. The sediment produced during this erosion is transported to basins (either river or ocean) where it is deposited. This deposition adds weight that causes the basin to sink so isostatic equilibrium is maintained. Based on diagrams of Tarbuck & Lutgens, 1976

19. Man Induced Vertical Movement
Slide PP This slide shows the settlement that occurred between 1935 and 1950 at Las Vegas, Nevada and in the vicinity of Lake Mead on the Colorado River upstream from Hoover Dam. Las Vegas settled a maximum of 340 mm and a large cone of depression centered on the lake sank 170 mm. The Las Vegas settlement was due to groundwater withdrawal while the Lake Mead settlement was due to the weight of add water when the lake was filled.
Adapted from USGS Circular 346, 1954

20. Ongoing Elevation Changes
Slide PP This slide depicts the present vertical movement within the U.S. (lower 48 states). There are three large areas of uplift They are 1) The Rocky Mtn. region (1-10 mm/year) caused tectonic (mountain building) activity; 2) Upper Mid-West (5-15 mm/year) caused by glacial rebound and 3) Southeast region (1-10 mm/year) caused buckling, weight removal and tectonic activity. Areas that are settling include: 1) East Coast (1-10 mm/year) caused by plate cooling along the Passive Margin; 2) Gulf Coast (5-10 mm/year) caused by weight from deposition of sediment in the Gulf of Mexico and 3) Central Valleys of California (5-10 mm/year) caused by Active Margin plate tectonics.

21. Active Margin Note: Aleutian Trench Canada Mobile Belt Deposits
Strike-Slip Faulting
Mobile Belt Deposits
California
Slide This slide shows the tectonic conditions along the Pacific Rim from Mexico to the Aleutian Islands. Most significant is the subduction along the Aleutian Island creating the Aleutian Trench and the Transform Boundary along the U.S. West Coast that contains the San Andreas Fault. Taken from Kious & Tilling, 1996, USGS

22. Active Margin Ocean-Continent Subduction Strike Slip Faulting
Slide PP This slide depicts the tectonic activity taking place along Washington, Oregon and California coasts. There is a subduction zone off Washington and Oregon coast. Numerous
Strike-slip Faults (Blanco, Mendocino, Murray and Molokai) occur in the ocean in this region. The San Andreas Fault which is the southern extension of the Mendocino Fracture Zone is the only Strike-slip Fault exposed on land in this area. Taken from Kious & Tilling, 1996, USGS

23. Hot Spot Locations
Slide PP Some of the more prominent hot spots on earth are shown on this slide. There appears to be no clear correlation between surface tectonic features and the hot spots. Hot Spots and created the Hawaiian Islands and the Yellowstone Park features in the U.S. Taken from Kious & Tilling, 1996, USGS

24. Hawaiian Hotspot
Slide PP The formation of the Hawaiian Islands by Hot Spot activity is illustrated in this slide. Note that the islands get progressively older to the north because the Pacific Plate is moving northward with respect to the subsurface thermal plume. Taken from Kious & Tilling, 1996, USGS

25. Passive Margin Coastline Sinking Drowned River Valleys
Numerous Near-shore Islands
Shoreline Migrating Landward
Slide PP This slide depicts the part of the South Carolina, Georgia and Florida coast that forms part of the East Coast Passive Margin. Most notable are the drowned river valleys; near shore islands and retreating shoreline that is caused by Plate settlement. Adapted from Zeigler, 1959

26. Northern Hemispheric Glacial Areas 16,000 B.P.
NOTE:
Portions Of Alaska
Are Ice Free
Slide PP This slide is a map centered at the North Pole that shows the extent of glaciers at the last glacial maximum 16,000 years ago. Note that significant portions of Alaska and Eastern Siberia were ice free even though all of Canada and Northern Europe were ice covered.

27. Pleistocene Glaciation
Note:
Alpine Glaciers
Continental Glaciers
Ice Marginal Rivers
Alaska Ice Free Area
Slide PP2.6-2 North American climate during maximum Pleistocene Glaciation 16,000 years ago are shown on this slide. Note the ice free areas in Alaska; the boundary between the Canadian Alpine and Continental Glaciers; the disturbed drainage pattern and the hot, dry area in southwestern U.S. The ice in the area between the two ice sheets became ice-free soon after the climate began to warm. This melting created an ice-free path from Eastern Siberia to the Lower-48-States. Adapted from Dott & Batten, 1971

28. Glacial Impact Areas
Slide PP The extent of areas impacted by glacial activity in the U.S. during the last four glacial periods are shown. Impacts are most extensive in the Great Lakes area while the glaciation was confined to mountainous areas in the West. Additionally numerous lakes (not shown on the slide) formed in closed basins in the West and along the ice margin. Water to fill the Western Lakes can from increased precipitation and runoff. The ice marginal lakes changed rapidly as the ice moved and new outlets formed. Sea level dropped more than 100 meters and the seafloor was exposed along the coasts. Note that the extent of exposed seafloor is much greater along the east coast than along the west coast. Adapted from Flint, 1971

29. Preglacial Teays Basin
Overrun By Ice
Channel Buried
Ohio River
Forms
Drains Basin
Slide This slide shows the disruption of the River Basins south of the Great Lakes caused by glaciation. The preglacial Teays River Basin was overrun by the glaciers and the stream channels filled with glacial debris. The Ohio River formed south of the ice sheets to carry off meltwater and now has became the river that drains the old Teays Basin.

30. Western Glacial Lakes 15,000 B.P. Climate Much Wetter Than Present
Large Basins Had Internal Drainage
Slide PP This slide shows the extent of lake formation in the Western U.S. during the last ice age 15,000 years ago. Note glacial lakes had two origins. The lakes depicted in this slide occurred because there were closed basins available to be filled the increased precipitation. Other lakes (not shown here) formed in ice-blocked river valleys along the glacial margin. Adapted from Flint, 1071

31. Loess Wind Blown Silt From Glaciers Stream Banks Stand Vertical
Rock Flour
Stream Banks Stand Vertical
When Stable
Slide PP Location and depth of wind-blown silt deposits (Loess) in Central U.S. are shown. These deposits are up to twenty meters thick and were derived from sediment blown off the floodplains of the Mississippi, Missouri, Illinois and Ohio Rivers. During glaciation these river systems carried vast amounts of water and sediment. Adapted from Skinner & Porter, 2000

32. Glacial Rebound Contours In Meters Uplift
Slide PP2.6-7 This slide is a map of Canada that shows the four major drainage provinces (Pacific, Artic, Labrador and Atlantic) and the extent of glacial rebound that has taken place in the last 10,000 years. There are two centers of rebound located on the east and west side of Hudson Bay. Uplift at each center has been about 100 meters. Adapted from various sources.

33. Great Lakes Glacial Rebound Contours – Uplift per 100 Yrs.
Slide PP This slide is a map of the Great Lakes region showing the water shed boundary (topographic divide) that determines what streams flow into the lakes; the numerous moraine features that are located south of the lakes and uplift rate contours for the ongoing glacial rebound. The rebound starts near the south shores of Lake Michigan and Lake Erie. The uplift rate steadily increases to the north-northeast until a rate of 1.75 feet uplift per 100 years occurs just north of Lake Superior. Base map adapted from Farrand, 1988 and Rebound Data from Clark & Persoage, 1970.

34. Sea Level Changes 16,000 Years BP -- 120 Meters Lower 6,000 Years BP –
Reached Present Level
Near Future –
Expected To Rise
Slide PP This slide shows changes in land area that was exposed in North America at different times. These changes are primarily due to sea level change. The conditions shown are: 1) Peak glacial 16,000 years ago when the oceans were 120 meters lower; 2) Present conditions and 3) at peak interglacial times when most of the world’s glaciers have melted. Because the climate is now warming, the land area exposed should start decreasing and approach peak interglacial conditions.

35. Holocene Sea Level Changes
Primarily Cause ---
Glacial Melting
In The
Northern Hemisphere
Slide PP This slide is a graph of Relative Sea Level versus Time (the last 18,000 years). Initially sea level raised rapidly but started to slow about 6,000 years ago. Note that most of this rise was caused by melting Northern Hemisphere Glaciers.

36. Erosion In River Basins
Controlling Factors:
Chemical vs. Mechanical Weathering
Temperature
Precipitation
Basin Gradient
Basin Soil/Bedrock Type
Tectonic Activity
Slide PP This slide summarizes the factors that control erosion in river basins.

37. Chemical & Mechanical Weathering
Slide PP This slide is a graph showing the relative importance of Mean Annual Temperature and Mean Annual Precipitation in determining whether Mechanical or Chemical Weathering will prevail. Higher temperatures and precipitation favor Chemical Weathering while colder temperatures and moderate precipitation favor Mechanical Weathering. Only slight weathering occurs when the climate is both hot and dry. Note that Mechanical Weathering is primarily caused by freeze-thaw action that forces small cracks in solid rock to expand thus breaking the material apart. Adapted from Peltier, 1950

38. Erosion Processes
Slide PP2.7-3 This slide is a diagram illustrating how changes in temperature change erosion rates for processes involving glaciers, wind, mass movement and water (rivers and streams). Cold conditions favor glaciers. Both mass movement and water caused erosion increase with higher temperatures but water caused erosion predominates in hotter conditions. Wind is an active but minor agent at all temperatures Adapted from Blumenstock & Thornthwaite, 1941

39. Erosion Processes
Slide PP2.7-2 This slide is a diagram illustrating how changes in precipitation change erosion rates for processes involving wind, mass movement and water (rivers and streams). Dry conditions favor wind. Both mass movement and water caused erosion increase with added precipitation but water caused erosion predominates in wetter conditions. Adapted from Blumenstock & Thornthwaite, 1941

40. Mass Movements
Slide PP This slide depicts the extent of two mudflows that originated on Mt. Rainier and flowed northwest into the Puget Sound area.
The Osceola Mudflow occurred about 5000 years ago and the smaller Electron Mudflow occurred about 500 years ago.
Topinka, 1997, USGS

41. Class Handout
Slide PP This slide shows Rates of Geologic Processes for various categories including Deposition, Erosion, Sea Level, Crustal (Tectonic) and Crustal (Glacial). The rates for the categories shown are listed in order of increasing rate that generally increase from meters/1000 years to 100 meters/1000years. Copyright Geomax, P.C. used with permission.

42. CASE STUDIES Columbia River Mississippi River Ohio River Potomac River
Red River of the North
Rio Grande River
Santa Ana River
Slide PPCS0.1 This slide contains a list of Rivers whose basins are to be studied. These systems were picked to provide a range of conditions and environments that can be encountered within the U.S.

43. Geologic Setting
Slide PPCS0.2 This slide lists some of the more significant Geologic factors that need to be considered for each of the River Basins included for case study.

44. JURISDICTION & CONCERNS
Slide PPCS0.3 This slide lists some of the more significant Non-Geologic factors that need to be considered for each of the River Basins included for case study.

45. Slide Presentation Prepared By Geomax, P. C. Dr. Donald R
Slide Presentation Prepared By Geomax, P.C. Dr. Donald R. Reichmuth, President 1023 W. 30th Ave. Spokane, WA Phone & FAX – –
This slide set for Session 2 was last edited on 8/4/04.