Exam Review and Rivers/Streams

Exam Missed Questions Review

  • Half-life of a radioactive parent isotope: The time it takes for half of the parent isotope to decay.
  • Death Valley sinking: Subsidence is the phenomenon of sinking due to the weight of accumulating sediments.
  • Alluvial fan: Sediment shed from a mountain, forming a fan shape with coarser materials at the top and lighter materials at the bottom.
  • Marble and quartzite: Non-foliated metamorphic rocks dominated by minerals with equant grains have no preferred orientation.
  • Regression: Occurs when land is uplifted by tectonic processes, causing coastal environments to migrate seaward.
  • Unconformity: Sedimentary rocks overlaying igneous and metamorphic rocks indicate a nonconformity (sedimentary rock on crystalline or metamorphic rock).
  • Beach environment: Typically composed of mostly coarse, well-sorted sediments.
  • Closure temperature: Represents the point when isotopes are no longer free to move in and out of the crystal lattice. (The isotopes do start to decay here.)
  • Well-sorted sandstone with asymmetric ripples: Most likely deposited as sand by a river.
  • Basaltic clasts within a conglomerate dated to 50,000,000 years: This age is likely too old for the conglomerate because the clasts are older than the conglomerate itself.
  • Organic matter in soil: Likely to be found in the O (organic) layer.

Rivers and Streams

  • Focuses on terrestrial environments; ocean environments will be covered later.
  • Topics: Terminology, water cycle, stream flow dynamics, erosion, stream types, deposits, and flooding.
  • Hundred-year flood: A flood event with a 1% probability of occurring in any given year, not an event that happens every 100 years. Statistically, there's a 26% chance of it occurring within a 30-year mortgage period.

Landscapes & Landforms

  • Landscape: The character and shape of a region (e.g., mountainous, desert).
  • Landforms: Individual features within a landscape (valleys, hills, mountains, beaches).
  • Geologic structures and topography are important in geology because the surface often reflects the subsurface.
    • Relief: The difference between the highest and lowest elevation points in a given area. Relief=Highestpoint−LowestpointRelief = Highest _point - Lowest _point; For example, in an area ranging from 0 to 300 meters, the relief is 300 meters. Streams flow downhill, so relief determines flow, velocity, and pathway.
  • Topographic maps: Use contour lines to represent fixed elevations. Closely spaced lines indicate a steep elevation change (resistant rock), while widely spaced lines indicate a gentle slope.
  • Erosion: The removal of the Earth's surface.
  • Deposition: The accumulation of sediments.
  • Relief affects deposition; low relief means deposition close to the source, while high relief allows sediments to be carried farther.
  • Erosional landforms: Buttes, plateaus, mesas (sediments are removed).
  • Depositional landforms: Formed by sediment deposition via wind, water, or evaporation (e.g., alluvial fans, desert lakes).
  • Factors controlling the landscape: erodent (wind, water), topographic relief, climate (dominant factor), substrate composition, life activity, and most importantly, time.

The Water Cycle

  • Evaporation carries water, leading to precipitation; runoff stays on the surface. Subsequent lectures will cover infiltration and groundwater.
  • Las Vegas water sources: Primarily from the Rocky Mountains via the Colorado River. This is dammed at Lake Powell, then released through the Grand Canyon into Lake Mead. Groundwater only makes up 10% of the water source.
  • Las Vegas Wash: Reclaimed water is treated and released, flowing through a bike trail.
  • Lake Mead: The spillway is no longer active. NASA observations show a substantial decline in water levels. Evaporation is a major concern, and proposals to use floating solar panels have been rejected due to recreational concerns.
  • Lake Mead Historic Water Levels: Show periods of filling and drought, with current levels approaching "dead pool." Three intake tubes have been installed, with the first now exposed. Intake 3 is ironically located near the Las Vegas Wash outflow.
  • Drought monitoring data (2023 vs. 2024) indicates that more areas are affected.
  • Conservation helps because population increasing, but water use is decreasing. Water is renewable but not equally distributed.
  • Hydropshere Breakdown
    • Freshwater: 2.5% of all water. 70% in glaciers/ice caps, 30% groundwater, 1.2% surface water.
    • Surface freshwater: 70% in ground ice/permafrost, majority in lakes. Other is in the atmosphere.
    • States water wars are likely.
  • Components: evaporation, precipitation, and runoff.
  • There are also relief changes. Erosion goes from high to low elevation.
  • The Moon lacks a hydrological cycle, so craters are preserved.

WATER USES

  • Water is important for food production, recreation, hazard mitigation, energy generation (dams), and health.
  • You can only servive for 3-5 days without water.

Water Sources & Stream Formation

  • Water evaporates, forms clouds, and precipitates, especially in mountains. A rain shadow can occur on the opposite side.
  • Take note of where the water table is to the stream: a stream with running water will be at the same level as the water table.
  • Channel Formation: Runoff combines into sheet wash, forming channels that remove sediments. It's a give-and-take relationship.
  • Headward Erosion: Channels lengthen by cutting back into the mountain. Waterfalls exemplify this process.
  • Tributary streams feed into the main channel.

Drainage Basins

  • A network that collects water from a broad region and drains it into a specific trunk stream. Drainage divides separate drainage basins.
  • Colorodo River divides into upper, lower, native tribes, and Mexico. Water rights are a major diplomatic and legal issue.
  • North America Continental divides separate the pacific from atlantic.
  • To construct a drainage Basin, follow these steps:
    • Find the outlet of the basin.
    • Mark stream paths.
    • Mark elevations using contours.
    • Connect ridges. Calculate areas via grid.

Drainage Network Patterns

  • Dendritic: The tree pattern; the most common. It's are flowing from multiple locations, i.e., sandstones.
  • Radial: Circular pattern coming off a mountain or volcano.
  • Rectangular: Flowing at right angles, using joints and fractures in a flat area.
  • Trellis: Parallels valleys and ridges/ cuestas.
  • Parallel: Uniform slope with very uniform patters, typical from steep terrain.

Streams

  • Permanent Stream: Flows all year round (fed by the water table).
  • Intermittent stream: Only flows occasionally, occurs where the water table is located below the stream level.
  • Measured by volume and velocityDischarge=width∗depth∗AverageVelocityDischarge = width * depth * Average Velocity and the units are m3s\frac{m^3}{s}
  • Discharge: Measured by width × depth × velocity (cubic meters per second).
  • Gradient: The change in elevation over distance. Higher gradient at the edges, coarser grain sizes.
  • Maximum water velocity is located toward the middle of the river.
  • Load: Material the stream carries.
    • Dissolved load: Ions.
    • Suspended load: Fine particles, floating.
    • Bed load: Coarse particles; rolling bouncing. SaltationSaltation bounces.
  • Competence: The maximum particle size a stream CAN carry. Can increase during floods events or decrease during drought.
  • Erosion: Kinetic energy of water is related to velocity and relief; erosion is highest where the kinetic energy is higher.
  • Niagara Falls: Example of headward erosion; water erodes shale and limestone, causing the falls to move back over time.
  • Water can erode due to abrasion and impact. Circular motions lead to potholes.
  • Stream Piracy: Occurs when headward erosion causes one stream to capture another stream's flow.
  • Pay attention and understand bold questions.

Stream Types & Deposits

  • Meandering Streams: Remove sediments from one side and deposit on a point bar. Oxbow lakes form when a meander is cut off from the main channel.
    • Point bars: The deposition from river bend.
    • An Ox Bow Lake forms from a stream cutting off a bend.
  • Rivers make bad borders due to erosion or deposition.
  • Braided Streams: Multiple channels interlaced with islands. Common in arid regions, glaciers, or after snow melt.
    • Aluvium occurs when these bars building up and dividing the river sections up.
  • Terraces: Uplift occurs from land being uplifting and incised down. Rapids form.
  • Gradient is increased along the mountains and hills where erosion happens.
  • Alluvial Fan: Fan-shaped structures at the edge of mountains due to sediment deposition because water slows down when opens up into a fan.
  • Delta: Deposits at the mouth of a stream at a coastal setting. Original delta looked like the Greek Delta.
    • New type called the birdesfoot delta.
    • Delta's evolve and grow over time.

Flooding Details

  • Floodplain: Low-lying areas where water accumulates during high-water events. Flood stages:
    • Normal stage: Water within.
    • Bank full. Is equal with the bank. Has a natural levee on the outer bend.
    • Flood stage: Overflows channel.
    • Oxbow lakes meander from it too. Oxbow lake occurs when river moves out before pinched off, so borders aren't good between each other.
  • Floods occur due to rain, snow, saturated soils.
  • Hundred Year Flood: A flood event with a 1% probability of occurring in any given year
  • Calculate Reoccurence: RI=N+1MRI = \frac{N + 1}{M} where N = Record of Number Years, M = Rank or number.
  • Do not buy property without being aware of the flood risk.