Exam 1 Flashcards
Im anxious so a lot of the card definitions are taken from this quizlet: https://quizlet.com/187042100/geomorphology-3300-exam-1-flash-cards/?i=4a1e89&x=1jqt
What are the differences between constructive, erosional, and mixed landscapes?
Constructive- material is being added.
Erosional- material is being lost
Mixed landscapes- Erosion and material being added
What are some examples of constructive, erosional, and mixed landscapes (conceptually; e.g. volcanoes
for constructive)? How are the three landscape types created or carved?
Constructive- volcanoes, deltas. Are built up from Earth’s surface
Erosional- Sandstone desert formations, canyons. Forms from the removal of Earth material.
Mixed landscapes- material accumulating at the base of a mountain. Forms by a combination of constructive and erosional.
What are physical/mechanical and chemical erosion? How do they differ?
Physical/mechanical erosion- Processes that weather landforms such, mostly water and wind. Freezing thawing also is mechanical erosion
Chemical erosion- Mostly water dissolving limestone through a chemical reaction. Limestone leaves as dissolved ions in the water
What rock is commonly worn away by chemical erosion?
Limestone
What differences are there between stable, steady-state, and unsteady landscapes?
Stable-essentially very little erosion (maybe 0.55 m every million years) (ex-interior of Australia stable due to low rainfall)
Steady state- (quasi equilibrium) constantly having to balance to steady position (ex-Cascade Range rate of mountain growth is equal to erosion)
Unsteady- change happening quickly and in or out unequal (ex-Liwu River Taiwan rock coming up very fast sometimes faster than soil can develop)
Know the three types of equilibrium and what each means.
Steady- static equilibrium. No change in channel gradient over short periods
Graded- steady-state equilibrium may show no change in gradient of channel
Cyclic- dynamic equilibrium. Gradual lowering of channel gradient over long time intervals
What are some very approximate erosion rates in stable, steady-state, and unsteady landscapes? Know
their order of magnitudes (e.g. mm/year or m/Ma).
stable- 0.55m/ma time basically meaningless
steady state- change happens 100-1000 years
unsteady- fast
Can you explain the concepts of equilibrium and disequilibrium using an example?
Equilibrium would be Cascade mountain range where the rate of mountain growth is almost equal to the rate of erosion
Disequilibrium- Liwu River Taiwan- Rock is being added so fast that soil cannot form
Why don’t potential energy and relief change in steady-state landscapes? Why DO they change in unsteady landscapes?
Potential energy and relief do not change because the height of landforms is not changing. Sharp elevation increases relief and potential energy
They do change in unsteady landscapes because elevation changes potential energy. Sharper slopes will have more potential energy and relief than previously smoother slopes
What do we mean by “rock in = rock out” in steady-state landscapes?
Rock in (construction) means that mass is being added to a landscape. Rock out means mass is being lost (erosion)
What is relief and how is it calculated?
The difference between a high point and lower elevation. High point minus low point
A retreating knickpoint lowers base level. How does this explain higher erosion rates downstream of the
knickpoint?
This lowering of base level increases the relief and therefore increases potential energy, which increases erosion
What are the three time frames we need to consider?
Steady- static equilibrium. No change in channel gradient over short periods
Graded- steady-state equilibrium may show no change in gradient of channel
Cyclic- dynamic equilibrium. Gradual lowering of channel gradient over long time intervals
How might landscapes be interpreted differently when viewed from the three different time frames?
There may be multiple steady states depending on which timeframe you use
Constant channel shape was assumed when modeling ancient floods at the location shown in slide 23.
This assumption was applied to a 2000-year-old flood. However, we noted that the river may not have looked the same 2,000 years ago. How might it have been different in such a way as to void Springer’s computer modeling of the flood?
Chanel migration from erosion and deposition; vegetation changes stabilizing banks; human activities; climate variability
Be able to define aggradation and incision.
Aggradation: Increase of land elevation due to depositing of sediment
Incision: Narrow erosion of stream to below base level
The river shown in the slides has multiple stable states (braided and single thread). How is this possible?
The channel gradient is remaining the same with fluctuations above and below the average condition
Be able to define: Variables, potential energy, longitudinal profile, gradient, threshold, braided channel, single channel
Independent variable: Intentionally changed/ controlled variable
Dependent variable: The result from independent variable
Quantitative variable: Numerical data from graphs or statistics
Qualitative variable: Concepts, thoughts, experiences from non-numerical data such as words, images, or videos
Potential energy: Stored energy depending on the position it has compared to other parts of a system
Longitudinal profile: shows distance vs elevation of a stream (upper point vs lowest point)
Gradient: Slope of a stream (rise/run)
Threshold: limits at which a system changes its state or behavior in response to environmental factors
Braided channel: Network of river channels separated by small, often temporary, islands
Single channel: i feel like this is self-explanatory but uhhh we ball
How and why do flood frequencies change because of urbanization?
Urbanization increases impervious surfaces (roads, buildings), reducing infiltration and increasing runoff, leading to more frequent and intense floods.
What are the processes by which water gets to channels and becomes runoff?
Precipitation → Infiltration (if soil is permeable) → Percolation → Groundwater flow → Baseflow
OR if the ground is saturated/impermeable: Precipitation → Surface runoff → Channel flow
What antecedent conditions are likely to generate floods?
High antecedent moisture, frozen ground, previous storms, saturated soils, deforestation, or urbanization reducing infiltration.
How do humans commonly decrease infiltration capacities?
Paving surfaces, compacting soil, removing vegetation, channelizing streams, constructing storm drains.
Explain the various factors that affect runoff production.
Precipitation intensity/duration, land use (urbanization, deforestation), soil type, slope, vegetation, antecedent moisture.
Why are hydrographs different in different parts of the same watershed?
Topography, soil type, land use, vegetation, and drainage patterns all influence how fast and how much water reaches the channel.
How do you read a hydrograph?
X-axis: Time
Y-axis: Discharge/ stage
Line: The response of the stream to excess water
What is stage?
The height of water in a river relative to a defined zero point.
How do you calculate flood recurrence intervals? Probabilities?
RI = (N+1)/M (N = number of years of data, M = rank of flood)
Probability (P) = 1/RI (ex: a 100-year flood has a 1% chance annually).
How do you read a graph of flood RI versus stage?
X-axis: Flood recurrence interval
Y-axis: River stage
Higher stage = rarer, larger floods.
What do we mean by transport-limited? Supply-limited?
Transport-limited: Sediment available but slow transport.
Supply-limited: Little sediment available despite high transport capacity.
How do alluvial and bedrock streams differ?
Alluvial streams: Flow through loose sediment, constantly reshape.
Bedrock streams: Flow over rock, erosion is slower.
Why are alluvial streams architects of their own geometry?
They adjust width, depth, and slope to balance sediment transport and water discharge.
Why doesn’t slope (So) decrease in bedrock streams when Q increases?
Resistant bedrock prevents easy erosion.
What defines bedrock streams?
Steep slopes, powerful floods, high erosion forces, limited sediment storage.
How do channel width, depth, gradient, and velocity change downstream?
Width & depth increase, gradient decreases, velocity stabilizes.
What are driving and resisting variables in streams?
Driving: Discharge (Q), slope (So
.
Resisting: Sediment size, vegetation, channel boundary resistance.
How do bedrock streams erode?
Abrasion, plucking, hydraulic action.
How do stream properties differ atop soft vs. hard rock?
Soft rock: Wide, meandering.
Hard rock: Narrow, steep.
What does an equilibrium profile look like; What does it look like in streams?
Smooth concave shape in alluvial streams. Energy In = Energy Out (balance between erosion & deposition).
What are knickpoints?
Abrupt changes in slope (e.g., waterfalls), often due to rock type changes.
What is shear stress?
Force of water on the bed that moves sediment.
What controls water velocities?
Discharge (Q), channel shape, slope, resistance from sediment.
Why is uplift a driving force?
Creates steep gradients, increasing erosion.
Why is channel boundary resistance a resisting force?
Harder materials slow erosion.
What are the three types of sediment load?
Dissolved load, suspended load, bedload.
What is d50?
Median grain size (50% of particles are smaller).
What drives/resists incision and sediment transport?
Driving: Slope, discharge.
Resisting: Bedrock hardness, sediment cohesion.
Why is drainage area a driver but median grain size a resistor?
Larger area = more water
Larger grain size = harder to move.
What are the inputs & outputs of a river system?
Inputs: Precipitation, erosion.
Outputs: Discharge, sediment transport
How does sediment move in floods?
Entrainment, rolling, bouncing, suspension.
Hjulstrom’s Curve shows sediment transport thresholds.
What is hydraulic radius (R) & unit stream power?
R = cross-sectional area / wetted perimeter.
High R → easier transport.
What is dynamic equilibrium in streams?
Balance between erosion, transport, and deposition.
What are the goals of soil mechanics?
Predict soil behavior for construction, agriculture, etc.
What is soil texture & angle of repose?
Texture: Sand, silt, clay mix.
Angle of repose: Maximum stable slope.
How does water affect soil stability?
Increases weight, reduces friction, adds cohesion.
What is stress & strain?
Stress = force/area, Strain = deformation.
How does pore pressure affect soil strength?
Increased pore pressure weakens soil.
What is soil grading?
Well-graded (mixed sizes) is stronger than uniformly graded.
What are the Atterberg limits?
Define soil behavior at different moisture levels.
What defines mass movement?
Gravity-driven downslope movement of earth materials.
What triggers landslides?
Heavy rain, earthquakes, deforestation, overloading slopes.
What are the five common mass movements?
Creep, slide, slump, earthflow, debris flow.
How to mitigate mass movements?
Drainage control, slope reinforcement, reforestation.
How do roads affect slope stability?
Increase runoff, disrupt natural drainage, trigger landslides.
How does energy loss due to eddy viscosity compare to energy loss caused by “innate” viscosities?
Energy loss due to eddy viscosity is generally larger than that caused by innate (molecular) viscosity because turbulence at larger scales dissipates energy more efficiently than molecular interactions. Eddy viscosity dominates in high Reynolds number flows, while innate viscosity is significant in low Reynolds number flows.
What forces operate on grains to resist and favor entrainment? See slide 45. Can you explain the various concepts like buoyancy or drag?
Forces resisting entrainment include gravity, friction, and cohesion, while forces favoring entrainment include drag, lift, and buoyancy. Drag pushes grains downstream due to flow velocity, lift reduces normal forces through pressure differences, and buoyancy reduces the effective weight of the grain in water.
How is shear stress related to the rate at which velocity changes above a streambed?
Shear stress is directly proportional to the rate of velocity change above the streambed, as described by the equation 𝜏= 𝜌𝑢∗^2, where 𝜏 (tau) is shear stress, 𝜌 (row) is fluid density, and 𝑢∗ is shear velocity. Greater velocity gradients near the bed result in higher shear stress, promoting sediment transport.
Why do we use the Shields Diagram instead of Hjulstrom’s? What are the variables in the Shields diagram and how are they related to individual grains?
The Shields Diagram is used instead of Hjulstrom’s because it accounts for dimensionless variables that apply across different flow conditions and grain sizes. It relates the Shields parameter (𝜏∗) to the Reynolds number of the grain, considering factors like grain size, density, and shear stress for more accurate sediment transport predictions.
Floods move sediment. How is sediment entrained or eroded? What is Hjustrom’s Curve? Which particle size is easiest to move? Why are clays hard to mobilize?
Floods entrain sediment when shear stress from flowing water overcomes resisting forces like gravity and cohesion, moving particles through rolling, saltation, or suspension. Hjulstrom’s Curve shows the velocities needed to erode, transport, and deposit different sediment sizes. Medium sand is the easiest to move because it lacks cohesion but is light enough to be lifted. Clays are hard to mobilize due to strong electrostatic cohesion, requiring higher velocities for erosion despite their small size.
Can you explain how and why w, h, and u are codependent such that streams maintain an average width and depth while constantly changing? Can you explain the example we covered in class?
Width (𝑤), depth (ℎ), and velocity (𝑢) are codependent because discharge (𝑄 = 𝑤 ⋅ ℎ ⋅ 𝑢) must remain balanced; when one variable changes, the others adjust to maintain equilibrium. For example, if depth decreases due to sediment deposition, velocity may increase to maintain discharge, preventing excessive widening or deepening of the stream.
What are the three types of stress and three types of strain?
Stress:
Compression – Forces push inward, shortening and thickening the material.
Tension – Forces pull outward, stretching and thinning the material.
Shear – Forces act parallel but in opposite directions, causing distortion.
Strain:
Elastic strain – Temporary deformation that reverses when stress is removed.
Plastic strain – Permanent deformation that does not return to the original shape.
Fracture (brittle strain) – The material breaks under stress.
Why are we typically most interested in the shear strength of earth materials when working on practical problems?
Shear strength is crucial because it determines the stability of slopes, foundations, and structures by resisting failure under stress. Understanding it helps engineers design safe embankments, retaining walls, and foundations to prevent landslides and collapses.
What are yield and rupture points?
The yield point is the stress level at which a material transitions from elastic deformation to plastic deformation, meaning it will no longer return to its original shape when stress is removed. The rupture point is the stress level at which the material breaks or fractures, marking the failure of the material.
What are the differences between stress axes s1 , s2 , and s3 ?
Stress axes s1, s2, and s3 represent the principal stresses in a material, with s1 being the maximum compressive stress, s2the intermediate stress, and s3 the minimum stress. These axes describe the orientation and magnitude of stress in a material, with each axis representing the direction in which the material experiences a specific stress (either compression, tension, or shear).
What combination of stresses causes shear to develop in solid bodies?
Shear stress develops in solid bodies when there is a combination of normal stresses (compressive or tensile) and differential stress (a difference between principal stresses). When two normal stresses are different in magnitude (shear stress is generated along planes oriented at 45° to the principal stress axes.
Friction (F) is proportional to the normal stress (σ) x friction coefficient (C): 𝐹 = 𝜎 ∙ 𝐶.
a. What is a normal stress?
b. Increasing the normal stress increases friction.
c. A sliding object experiences shear stress between itself and the underlying surface.
Normal stress (𝜎) is the force exerted per unit area perpendicular to a surface, either compressive (pushing inward) or tensile (pulling outward). It acts normal (or at a right angle) to the surface.
Define soil.
Soil is a naturally occurring, loose mixture of mineral particles, organic matter, water, and air, capable of supporting plant life and providing a habitat for organisms.
What factors control soil development (5)? CLORPT!
C: Climate
L: Organisms (including plants and animals)
O: Relief (topography)
R: Parent material
P: Time
How do each of these factors contribute to soil development?
Climate (C): Affects weathering rates, moisture, and temperature, influencing soil formation and properties.
Organisms (L): Plants, animals, and microorganisms contribute organic matter and influence nutrient cycling.
Relief (O): Slope and elevation affect water drainage, erosion, and accumulation of materials
Parent material (R): The mineral composition of the original material from which soil forms affects soil texture and mineral content.
Time (P): Soil formation takes time, with older soils often being more developed and having more horizons than younger soils.
Know the soil horizons and what happens in each.
O Horizon: Organic layer, composed mainly of decomposed plant material and organic matter.
A Horizon: Topsoil, a mix of organic material and mineral particles, supporting plant life.
E Horizon: Eluviation (leaching) layer, where materials like clay and minerals are washed out.
B Horizon: Subsoil, where materials leached from the above layers accumulate (illuviation).
C Horizon: Weathered parent material, consisting of partially disintegrated bedrock or unconsolidated material.
R Horizon: Bedrock, the unweathered base material beneath the soil.
What is saprolite and how does it differ from soil? From bedrock?
Saprolite is a weathered, soft, and partially disintegrated bedrock, often rich in clay minerals. It differs from soil because it lacks significant organic matter and has less biological activity. It differs from bedrock because it has undergone weathering but has not yet been broken down into fully formed soil.
What three particle size classes are typically included in soil?
Sand (0.05 – 2.0 mm)
Silt (0.002 – 0.05 mm)
Clay (less than 0.002 mm
How can soils be acidic? How is this related to weathering?
Soils can be acidic due to the presence of hydrogen ions (H⁺), often resulting from the weathering of minerals, especially those containing calcium, potassium, or sodium. Acidic soils are also linked to organic acids from plant decay and microbial activity.
Why do we refer to clays as secondary minerals?
Clays are referred to as secondary minerals because they form as a result of weathering and alteration of primary minerals (like feldspar or granite) over time.
How are 1:1 and 2:1 clays different?
1:1 clays (e.g., kaolinite) have one tetrahedral layer and one octahedral layer. They are stable, non-expanding, and have low cation exchange capacity (CEC).
2:1 clays (e.g., smectite) have two tetrahedral layers and one octahedral layer. They can expand and contract, have higher CEC, and are more reactive.
How do kaolinite and smectite behave differently when wetted and dried?
Kaolinite does not expand or contract significantly when wetted and dried, remaining stable.
Smectite expands when wetted and shrinks when dried, leading to changes in volume and structure.
Why are cations attracted to clay surfaces (e.g., calcium)?
Cations are attracted to clay surfaces due to the negatively charged sites on the clay particles (often from the isomorphous substitution of cations in the clay mineral structure), which attract positively charged ions like calcium (Ca²⁺).
What two components contribute to a soil’s cation exchange capacity?
Clay content: The higher the clay content, the greater the surface area for cation exchange.
Organic matter: Organic particles, especially humus, have many negatively charged sites that increase cation exchange capacity.
What are vertisols and how do they form and behave?
Vertisols are clay-rich soils that expand when wet and shrink when dry, causing cracks to form. They typically form in areas with pronounced wet and dry seasons, where the alternating moisture content leads to swelling and shrinking of the clay particles.
What causes vertisols to “churn” and how is this related to gilgai?
Vertisols “churn” due to the expansion and contraction of clay minerals with moisture changes, causing the soil to shift and form small, uneven mounds and depressions. This is related to gilgai, which are small, irregular surface features (micro-relief) created by the swelling and shrinking of these soils.
