GEOSC 10: Geology of the National Parks

Tearing Down Mountains II:Groundwater and Rivers

Presented by Dr. Sridhar AnandakrishnanThe Pennsylvania State University

GEOSC 10 - Geology of the National Parks

Water

•Falls from the sky

‣ Plants and trees drink & evaporate 2/3

•Some runs off into streams

‣ Streams carry water & sediments

•Some is soaked into the Earth to make groundwater... which eventually goes to streams

•Groundwater makes caves and drinking water

•Streams go to rivers go to ocean goes up into air

GEOSC 10 - Geology of the National Parks

Hydrologic Cycle

GEOSC 10 - Geology of the National Parks

Water

•Unique to Earth

‣ Maybe some on Mars, Moons of Jupiter

‣ Life needs water

•2/3 of Earth’s surface is water

•97% of Earth’s water is in the oceans

•Most of the rest in glaciers

•Water is most important surface processmodifying the landscape

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

Johnstown

GEOSC 10 - Geology of the National Parks

Streams Change Landscape

•Streams erode their bed

•Move water (duh) and sediments, boulders, all sizes of rocks in between

‣ Sediment is relatively finely ground up rock

‣ When rivers deposit sediment they do it in flat layers

•Floods do most of the work

GEOSC 10 - Geology of the National Parks

Human Uses

•Agriculture & industry

‣ Irrigation & transport

•Commerce

‣ Travel & trade

•Hydroelectric power

‣ Norway is rich because they don’t use oil (but have lots)

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

Hydrologic Cycle

•Water evaporates from the ocean...

• It rains onto land

‣ It evaporates right away

‣ Plants take up and then release into atmosphere

‣ 2/3 of rainfall goes straight back up

‣ This is evapo-transpiration

•Rest goes into streams and ground water

GEOSC 10 - Geology of the National Parks

Streams

•Driven by gravity

‣ Sea level is where water is heading (it can’t get lower)

•Recharged by direct rainfall

•Also by groundwater springs

‣ That’s why rivers run even after long periods without rain

GEOSC 10 - Geology of the National Parks

Erosion

•Streams carry sediments along with water

•Mass wasting (last time) delivers sediments to river

‣ That makes it higher and higher (at the place where mass wasting is adding stuff)

‣ That makes the stream steep

‣ That makes the water flow faster

•That carries away sediments!

GEOSC 10 - Geology of the National Parks

Moving Sediment

GEOSC 10 - Geology of the National Parks

Moving Sediment

•Suspended load

‣ Fine stuff floating up in water

•Bed load

‣ Bigger rocks (gravel to boulders) that bounce along

‣ Breaking up other rocks as they go, making smaller rocks

GEOSC 10 - Geology of the National Parks

Types of Streams

•Meandering streams

‣ If the river has mostly fine sediments, it makes a deep channel (it won’t get clogged)

‣ If it has a curve, the curve gets more pronounced

- Water on the outside of the curve has to go faster, so it erodes more, so it makes the curve deeper...

‣ Sometimes makes a big loop that gets cutoff: an oxbow

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

Braided Stream

• In areas with lots of gravel and boulders, the main channel gets choked

•New channels form all the time

•Looks like a braid from above

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

Dams

•A dam stops water temporarily but sediments permanently

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

Dams

•Sediments fill up the reservoir above the dam

•The river below the dam is clean of sediments, so that clean water can pick up more sediments

‣ If no dam, the water would be “dirty” - lots of sediments, so not so good at erosion

•Gravel and sand bars below dams get washed away

‣ Lots of critters live on those bars...

‣ Also, the clean water makes life tough forsome fish (they can’t hide)

GEOSC 10 - Geology of the National Parks

Dams

•Eventually that reservoir above the dam will fill up

GEOSC 10 - Geology of the National Parks

Katrina

•Levee protecting New Orleans broke

•New Orleans is below sea level, so water rushed in

GEOSC 10 - Geology of the National Parks

Floods

•Floods happen. Every year. Snowmelt, rains...

•When rivers flood they carry water and sediment out into the fields beyond the main channel

•But we don’t like mud in our living room...

‣ Ask the government to build walls preventing flooding, called levees

‣ Levees built over the last 100 years

GEOSC 10 - Geology of the National Parks

Big Easy...

•Big Easy built on mud from long agofloods

•Water is slowly squishing out and the mud is compacting

•New Orleans sinks, but Mississippi (also known as Big Muddy) stays the same...

•Eventually Big Easy lower than Big Muddy

•Stage set for disaster

GEOSC 10 - Geology of the National Parks

As if That Isn’t Bad Enough...

•Usually big rivers build natural levees

‣ Floods deposit more stuff near the river than far away, making a low wall...

•So for a while the river stays in one course...

•But eventually, during a big flood it will breach the levee and take a different course to the ocean

•All the riverbanks downstream of that breach are left high and dry

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

GEOSC 10 - Geology of the National Parks

Groundwater

•Soil is like a sponge

‣ Spaces between the grains can be filled with air or water

‣ Below a line called the water table, the spaces (pores) are filled with water. Above, they are mostly air.

•Rain seeps into the ground and slowly makes its way deep into the Earth

‣ Because water has to trickle through small pores, soil is like a natural filter - bacteria can’t get through

‣ Water trickles slowly, so bacteria die over time

‣ We can pump that water and drink it!

GEOSC 10 - Geology of the National Parks

Groundwater Pollution

•Soil is like a sponge

•Pour a chemical into the soil (motor oil, dry-cleaning fluid), and it is very difficult to get it out

•Think of a sponge. Add soap - you need to soak and rinse many many times to get all the soap out...

GEOSC 10 - Geology of the National Parks

Caves

• In State College, lots of limestone

•Groundwater is slightly acidic (critters in the ground breathe in oxygen and breathe out CO2)

•Water + CO2 = carbonic acid - a weak acid that dissolves limestone

•Water seeping into cracks will enlarge those cracks, making caves

•Now water can go deep quickly!

GEOSC 10 - Geology of the National Parks

Sinkholes

• If a cave forms near the surface, the roof can collapse, or it can fill with sediment

•Putting a big building (or road) on a sinkhole costs lots more...

•Memorial Field (State High football field) is a sinkhole

GEOSC 10 - Geology of the National Parks

Water Supply Pollution

• In areas with lots of limestone, we get caves (know as karst regions, after the region in Slovenia where this is common, and first noted)

•Water can go into caves (and sticks and leaves and bacteria) - no filtering

•Water can go quickly into the Earth - bacteria don’t die

•Water can be unsafe...