RIVERS,GROUNDWATER,

AND GLACIERS

Delta

A fan-shaped deposit that forms when a river flowsinto a quiet or large bodyof water, such as a lake, an ocean, or an inland sea.

Alluvial Fan

A sloping triangledeposit of sedimentlocated 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

Gradient or Slope

Discharge

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 riverand is covered byits water during a flood.

Meandering Rivers: •are rivers that develop broad, looping bends over time.•They shift there course across a valleyFloor 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

Four 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)

PorosityPorosity 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- Virginia Karst

eeer

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

• Bedrock Scour

Deposition

• Till

• Outwash

• Varved Clays

Meltwater Erosion

Glacial Deposits

River and Glacial Valleys