RIVERS, GROUNDWATER, AND GLACIERS
Delta A fan-shaped deposit that forms when a river flows into a quiet or large body of water, such as a lake, an ocean, or an inland sea.
Alluvial Fan A sloping triangle deposit of sediment located where a mountain stream meets level land.
Tributary A stream that runs into another stream or river.
Drainage Basins separated by high elevations
Drainage Basin
Mississippi River Drainage Basin
Characteristics of Streams and Rivers The ability of rivers to erode and transport sediment is affected by many characteristics that are interconnected. Stream/river velocity Stream/river gradient Stream/river discharge Channel shape
Stream Velocity
Formation of sand bars and cut-banks in meandering rivers
Discharge
Gradient or Slope
Channel
Stream Erosion and Deposition
Stream Velocity
Turbulent flow-decreased velocity caused by objects in stream and shape of banks
Floodplain A wide, level area that borders a river and is covered by its water during a flood.
Meandering Rivers: are rivers that develop broad, looping bends over time. They shift there course across a valley Floor over time causing it to widen Unique Feature of Meandering Rivers: Oxbow Lakes: a crescent-shaped body of water formed when sediments deposited by a river cuts off a meander from the river.
Horseshoe Falls
Stages of River/Stream Development
The Ideal Stream Cycle (W.M. Davis, 1880) Not a Literal Time Sequence Youth Maturity Old Age Rejuvenation
Youth V-Shaped Valley Fast Current Pot holes common Rapids Waterfalls No Flood Plain Drainage Divides Broad and Flat, Undissected by Erosion Valley Being Deepened
Maturity (Early) V-Shaped Valley Beginnings of Flood Plain Sand and Gravel Bars Sharp Divides Relief Reaches Maximum Valleys stop deepening
Maturity (Late) Valley has flat bottom Narrow Flood Plain Divides begin to round off Relief diminishes Sediment builds up, flood plain widens River begins to meander
Old Age Land worn to nearly flat surface (peneplain) Resistant rocks remain as erosional remnants (monadnocks) Shallow gradient Slow current Rivers meander across extremely wide, flood plains Ox bow lakes Levees Deltas
Rejuvenation Some change causes stream to speed up and cut deeper. Uplift of Land Lowering of Sea Level Greater stream flow Stream valley takes on youthful characteristics but retains features of older stages as well. Can happen at any point in the cycle.
Rejuvenation of an old-age landscape
Rejuvenation of an early mature landscape
Arid and Humid Weathering Compared Humid Climates Arid Climates Rainfall Frequent Rare, May Be Seasonal, Often Violent Soil Cover Thick Thin or Absent Vegetation Thick Sparse-no Continuous Cover Chemical Weathering Intense Weak Overall Landscape Evolution Mostly Uniform Processes Episodic Processes
Arid Erosion Cycle: Youth V-shaped Valleys Divides Flat, Undissected Much Like Youth in Humid Climates
Arid Erosion Cycle: Maturity Slopes Stay Steep, Retreat Alluvial Fans Playa Lakes Pediments
Arid Erosion Cycle: Old Age Inselbergs Playa Lakes Pediplain
River meanders across floodplain Base level drops, or region uplifts. Terrace forms in floodplain Further incision cuts a new terrace
A flight of river terraces
River and Glacial Valleys V-shaped U-shaped
River and Glacial Valleys
Groundwater
Groundwater is water that completely saturates (fills) the pore spaces of soil or rock formation below the water table. Water that shares pore space with air is called soil moisture.
Groundwater is the largest resevoir of fresh water that is readily available to humans
Soil moisture, and water vapor 1.2
Five factors that influence the rate at which water enters the groundwater system 1. Type of rock or soil 2. Climate (in dry areas, a lot of water evaporates before it soaks into the ground.) 3. Topography (steep slopes = runoff) 4. Vegetation (more vegetation = more water stays where it lands) 5. Land Use (human factors) development/pavement decreases absorption
Porosity Porosity is percentage of total volume of rock or sediment that consists of pore spaces.
Factors that affect porosity Particle shape (round sediments have more pore spaces than angular sediments) Sorting (poorly sorted sediments have fewer spaces than well-sorted sediments, because smaller pieces fill the spaces between bigger ones)
Permeability Permeability is the ability of water to flow through a rock or sediment layer, and the rate at which it does so.
Factors that affect permeability Pore Size- larger the pore space are, the easier water passes through. Clay and silt-sized sediments can be impermeable, because their shape allows them to overlap one another like stacks of paper. Interconnection of Pores- Pumice is not permeable because, although it is very porous, its holes are not interconnected. Presence of cracks in rock layers
Water Table zone of aeration zone of saturation
What Factors affect the Water table? Amount of Rainfall-more rain = higher water table Amount of time between rains Season Slope Soil thickness Climate How much water is being removed
Aquifer An Aquifer is an underground layer of water-bearing, permeable rock, or unconsolidated sediment, from which groundwater can be easily extracted.
Confined Aquifer Gravitational pressure
Perched Aquifers (unconfined)
Karst Aquifer Loudoun County, VA
Geyser
Artesian Well Artesian formation: An arrangement of permeable layer of rock sandwiched between two layers of impermeable rock.
Groundwater Contamination
Saltwater Intrusion
Karst Topography Karst is a topography in which the landscape is largely shaped by the dissolving action of acidic water on carbonate bedrock (usually limestone, dolomite, or marble). This geological process, occurring over many thousands of years, results in unusual surface and subsurface features ranging from sinkholes, vertical shafts, disappearing and emerging streams, and springs, to complex underground drainage systems and caves. Karst provides water for many Virginians.
Vertical Shafts
Underground Rivers
Caves
Sinkholes
Karst Counties in Virginia
West- eeer Virginia Karst
Glaciers
Glacier: a Flowing Stream of Ice There are two types of glaciers: Mountain Continental (Greenland, Antarctica)
Mountain Glacier Landforms
Continental Glacier Landforms
Snowfall vs Melting & Evaporation (Ablation) Zone of Accumulation Snowfall Exceeds Melting & Evaporation Excess Snow Turns to Ice & Flows Out Zone of Melting or Ablation Melting & Evaporation Exceeds Snowfall Melting Excess Made up by Ice Flowing in Terminus of Glacier Snowfall & Inflow = Melting & Evaporation (Ablation)
Anatomy of a Glacier
A Typical Glacial Advance and Retreat
As long as Accumulation = Ablation, the Glacier Front Remains Fixed
If Accumulation Exceeds Ablation, the Glacier Advances
If Ablation Exceeds Accumulation, the Glacier Retreats
Results of Glaciation Abrasion Polish Striations Chatter Marks Crescentic Gouges Deposition Till Outwash Varved Clays Meltwater Erosion Bedrock Scour
Glacial Deposits
River and Glacial Valleys