Including...
Introduction
Weathering
Mechanical
Biological
Chemical
Decomposed Granite
Erosion
Falls, Slides, and Flows
Complex Movements
Creep
General Review: a regional view
Earth has 2 levels
Earth has 2 types of rock
Earth has 2 processes
Construction and Destruction
Over the course of geologic time these 2 are in balance
Tectonics: the study of earth processes which result in the creation and deformation of magma and rock
This builds the earth as we know it (videodisc of mountains)
The destructional processes are covered in "The Hydrosphere"
This stuff can be mighty impressive
Carve valleys (get videodisc - rivers and glaciers)
Wash to sea (beach shots with sand/gravel)
The basic idea: the earth takes what it builds and puts it in the ocean (overhead)
But first the earth has to break it up because the mountains are too big to move in one piece
Mechanical (physical) weathering
Smaller pieces / same stuff
Fracturing and Abrasion
Like the difference between a hammer and sandpaper
Results in clastic sediments
Sands to conglomerates
Lots of methods
Rocks in river
Rocks falling
Ice - the big one
Cold areas with large daily temperature fluctuations
Ice wedging: expands 10% upon freezing
Can exert up to 4,900,000 lbs./in^2!!
Makes angular fragments and surfaces
Tree roots can grow into cracks - force them apart
Biologic acids can "eat" the minerals
Over the course of geologic time everything gets dissolved (overhead)
Minerals dissolve when exposed to water and heat
Smaller pieces AND different stuff
Water need to be able to touch the minerals
Surface area VERY important!
EXPLAIN FULLY
High temperatures also act as a catalyst
Hot humid areas best for chemical weathering
Makes rounded fragments and surfaces
Do a lab on this tomorrow
Chemical weathering lab
It's like a cycle (remember the hydrologic cycle? Same idea)
Story of Decomposed Granite (or What's really happening below your feet)
Biologic / physical (EX: tree roots in cracks)
Biologic / chemical (EX: root acids)
Chemical / physical (EX: granite)
Physical / chemical (EX: Fracture and abrasion lead to inc. surface area)
Abrasion and "rock flour"
Chemical / biological (EX: leads to soil formation)
And back to biologic weathering
Movement of material downslope under the influence of gravity
Water acts as catalyst and lubricant
Factors that affect erosion include
Climate
Saturation of surface materials
Type of material at and near the surface
Vegetation
Degree of weathering
Steepness of slope
DIGRESS TO: Angle of Repose
Earthquake activity
Human disturbance
Becomming increasingly common as we build on steep and/or unstable slopes
Can be nearly imperceptible to extremely spectacular events
Rockfalls-vertical to near vertical
Common in alpine regions where ice wedging is prevalent
Result in Talus Slopes at base of cliff
Can result in flooding if they fall into a lake
Slides - broad term covering several types of downslope movement
Often the result of human disturbance
Lahars - volcanic mudflows
Like the debris flow from Mt. St. Helens
Complex movements - combination of processes
Nevado Huascarán, Peru: May 31, 1970
Large earthquake shakes loose 50 million cubic yards of ice, snow, and rock
Free-fall 3000 feet
Then down-valley at speeds up to 200 mph (how fast can YOU run)
Over-topped ridges >400 feet high
Roared into the town of Yungay - killed >20,000 residents
Continued downslope to Ranrahirca where it buried 5,000 more
Only part of Yungay not buried was "Cemetery Hill"
92 people survived by running to the top
One survivor states (with minor editing) "As we drove past the cemetery the car began to shake it was an earthquake. We stopped the car and got out to observe the damage around us. We saw several homes near to us collapse from the shaking. The quake lasted for 30 to 45 seconds. When it was over I heard a great roar coming from Huascarán. Looking up I saw a cloud of dust and it looked like a large mass of ice and rock was breaking loose from the north peak. My immediate reaction was to run for the high ground of Cemetery Hill. Part way up my friend fell and I turned to help her back to her feet.
"The crest of the wave (of debris) had a curl, like a huge breaker coming in from the ocean. I estimated the wave to be at least 250 feet high. I observed hundreds of people running in all directions, many towards Cemetery Hill. All the while, there was a continuous loud roar and rumble. As I reached the top and turned, I saw a man about 10 feet down the hill who was carrying 2 small children. The debris flow caught him and he threw the 2 children toward the hilltop to safety, but the debris flow swept him away. The same wave also swept away 2 women near to him, and I never saw any of them again. It was the most horrible thing I have ever experienced and I will never forget it."
Creep - affects the topmost layer of soil/debris
Anything which disturbs the surface of the land causes creep
Ice needles, people, wind, rain drops, ants, bunny farts, anything!
Results in the upper surface "creeping" downslope
Pistol butt trees common due to creep
Seems like no big deal, but
Radius of earth = 3963.5 miles = 20,927,280 ft.
Surface area of a sphere = 4 pi r^2 = 5.5 X 10^15 ft^2
Total area above sea level (29%) = 1.6 X 10^15 ft^2
Divided by 9 ft^2 per yard^2 = 1.77 X 10^14 yds^2
If it is all involved to a depth of 0.0001 yard
1.77 X 10^14 yds^2 X 0.0001 yard = 1.77 X 10^10 yds^3
Assume that 10% is involved in any given minute
1.77 X 10^10 yds^3 times 0.10 = 1.77 X 10^9 yds^3 per minute!
Or 2.55 X 10^12 yds^3 per day
Most books stress large rockfalls and mudslides, and say that they stagger the imagination. So does creep!!