Tearing Down Mountains II: Groundwater and Rivers

1. Tearing Down Mountains II:Groundwater and Rivers • Presented by Dr. Sridhar Anandakrishnan • The Pennsylvania State University

2. 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

3. Hydrologic Cycle

4. 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

6. Johnstown

7. 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

8. Human Uses • Agriculture & industry • Irrigation & transport • Commerce • Travel & trade • Hydroelectric power • Norway is rich because they don’t use oil (but have lots)

10. 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

11. 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

12. 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!

13. Moving Sediment

14. 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

15. 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

19. 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

22. Dams • A dam stops water temporarily but sediments permanently

24. 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)

25. Dams • Eventually that reservoir above the dam will fill up

26. Katrina • Levee protecting New Orleans broke • New Orleans is below sea level, so water rushed in

27. 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

28. 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

29. 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

32. 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!

33. 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...

34. 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!

35. 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

36. 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...