Weathering, Soils and Groundwater

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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The Rock Cycle

The Ideal Rock Cycle

Anything can happen in the Rock Cycle


Weathering

Breakdown of Rock near the Surface Due to Surface Processes

Mass-Wasting

Movement of Large Amounts of Material Downhill under Gravity


Surface Area and Weathering

Imagine a cube of rock one meter on a side:

Thus:

-- Divide the edges by 2, total area increases 2 times
-- Divide the edges by 3, total area increases 3 times
-- Divide the edges by n, total area increases n times

For a one-meter block crushed into 0.1 mm pieces, the edge length is divided by 10,000, and the area multiplied by 10,000. 10,000 square meters is over 100,000 square feet or 2-1/2 acres.

Surface-Volume Effects

The smaller we subdivide particles, the more surface area is exposed. Things that happen at surfaces, like heat transfer or chemical reactions, happen faster. Some common applications of this fact:

A more serious example:

Flour in a sack in your kitchen is about as inert as a material can get. Grain dust (which is what flour is) dispersed in the air is highly combustible, even explosive. Every year a couple of dozen people in the U.S. die in grain elevator explosions caused by suspended dust. Coal dust in mines can be even deadlier.


How Surface-Volume Ratio Affects Weathering

Hence: corners of blocks weather fastest, then edges, then faces. The interior is immune as long as the surrounding material is intact.

What Determines Soil Type


Soil Formation

Young Soils

Strongest Influence Is Parent Material

Mature Soils

Strongest Influences:Climate, Vegetation, Drainage

Processes

Leaching from Surface

Accumulation beneath Surface


Soil Horizons and Profiles

Soil Horizons

Layers in Soil
Not Deposited, but Zones of Chemical Action

Soil Profile

Suite of Layers at a Given Locality

Limits of Soil Formation


Soil Classification

This may be the most difficult classification problem in science because of the many factors involved.

Multiple Objectives

Scientific

Genesis & Evolution

Agricultural

Engineering

Varied Bases for Classification

"The 7th Approximation"

Groundwater

The Hydrologic Cycle



Aquifers



Green Bay Case Study


Deep Aquifers of the Green Bay Area



Green Bay Groundwater Pumping 1880-1960



Green Bay Water Table 1880-1960

The recharge zone for the deep Cambrian sandstone aquifers is near the Wolf River, at an elevation more than 50 m above Green Bay. Thus, the deep aquifers were originally artesian, and the piezometric surface was up to 25 m above ground level. By about 1910, the groundwater had been depleted so much that the piezometric surface was near ground level and suction pumps had to be installed. Suction pumps will lift water only about 10 m, the height of a water column that equals atmospheric pressure.

By the 1920's the piezometric surface had fallen an additional 10 m and turbine pumps had to be installed. The piezometric surface continued to plummet until 1957, when Green Bay ceased municipal pumping and began drawing water from Lake Michigan. The piezometric surface recovered rapidly.


Green Bay Piezometric Surface

The piezometric surface just as pumping ceased. A classic cone of depression. The piezometric surface a couple of years after pumping ceased. Note the dramatic but not complete recovery, since there is still a good deal of private pumping and municipal pumping outside Green Bay.


A comparison of water use and piezometric surface 1920-1960. Note that when the city of Green Bay stopped pumping, water use dropped to levels of about 20 years earlier, and the piezometric surface rose to levels of about 20 years earlier.


The Russian Radioactive Waste Injection Program

Graphics based on illustrations in The New York Times.

The waste is injected into porous sandstones beneath impervious clay layers. The geology seems pretty well suited to this sort of system but the waste is spreading faster than expected. It is entirely possible the waste will never escape, or escape after such a long time that most of the radioactivity has died away. However, if it does escape, the results could be bad.

Mass Wasting

Viaont, Italy, October 9, 1963

VAIONT.GIF (6842 bytes)
The nearly 300-meter tall Vaiont Dam was the tallest in Europe when it was completed. In the fall of 1963 heavy rains weakened a shale layer south of the reservoir. On October 9 the shale gave way and the overlying layers slid downhill into the reservoir. The dam, amazingly, was undamaged. Instead, water from the reservoir was simply pushed up the opposite valley wall and around the dam. The first casualties were some dam workers staying in a hotel 300 meters above the dam. The water then poured down-valley, wiping out the village of Longarone and several smaller villages. 1800 people died.

Yungay, Peru, May 31, 1970

YUNGAY.GIF (7020 bytes) A magnitude 8 earthquake triggered a huge avalanche from the summit of Nevado Huascaran, the highest peak in Peru. Part of the landslide jumped a 200-meter ridge, wiping out the town of Yungay and killing all but about 100 of its 20,000 inhabitants. This is the worst avalanche disaster in history.

In addition, the earthquake killed another 50,000 people elsewhere in Peru. The total death toll of about 70,000 makes this the worst natural disaster ever in the Southern Hemisphere.

Sherman Glacier, Alaska, March 27, 1964

SHERMAN.GIF (4022 bytes) The great Good Friday earthquake of 1964 triggered a large rock avalanche that fell 600 meters (2000 feet) and then spread 5 km (3 miles) across the Sherman Glacier, resulting in a blanket 3-6 meters (10-20 feet) thick. The avalanche is dramatically visible because it contrasts with the white glacial ice. The drawing at left is based on a photograph. The flow ridges and lobes are characteristic of large avalanches.

Lituya Bay, Alaska, July 9, 1958

A magnitude 7 earthquake on the Fairweather Fault (Southeast Alaska's equivalent of the San Andreas) triggered a landslide that dropped into a glacial bay (fiord). The resulting wave washed away the forest on the opposing side to a height of 1720 feet, the highest known wave ever documented.

LITUYA.GIF (8344 bytes) Note from the sketch map that this is extremely rugged terrain. Elevations rise from sea level to over 2000 feet in half a mile, a slope of nearly 45 degrees in places.

References

Don J. Miller, 1960; Giant Waves in Lituya Bay, Alaska, U.S. Geological Survey Professional Paper 354-C, 86 p. Good luck finding this. It tends to disappear from libraries. I bought what may have been the last available copy.


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Created February 3, 1997, Last Update 23 January 2001

Not an Official UW-Green Bay Site