Next on the agenda: CLAYS: Where it's all happening!

Secondary Minerals: the Clays These are SHEET SILICATES composed of stacked tetrahedral layers and octahedral layers ( = silica sheets and alumina sheets). These can be stacked in a ratio of 1:1 or 2:1. In most real clays, minor Al for Si substitution in the tetrahedral layers gives them a small (-) net charge The 2:1 clays are most typical of areas with limited water availability.

These clays can ALSO be either DI- or TRI-octahedral: e.g., Kaolinite is DIoctahedral - only 2/3 of octahedral sites are occupied, by trivalent (+3) cations - like Al +3, Fe +3 ; Mn +3, Cr +3, B +3 etc., can also fit here. xx x = M +2 if red dots instead represent other divalent cations TRIoctahedral clays have all three sites occupied, but by divalent (+2) cations. So, the net charge for three octahedral sites remains at a total of +6. TRIoctahedral clays have all three sites occupied, but by divalent (+2) cations. So, the net charge for three octahedral sites remains at a total of +6.

The unit of measurement is milliequivalents/100 grams (abbreviated meq/100 gm), where 1 meq= x 1 gram-equivalent weight ÷ the cation charge. For potassium (a.w.= ~39) (as K + ): 1 gram-equivalent-weight = 39 grams; 1 meq = gm For calcium (a.w. ~40)(as Ca +2 ): 1 meq = 0.040÷2 = gms. A clay with a CEC of 10 means it can potentially hold 10 meq of cations loosely on and/or in its structure per 100 grams of clay. The CATION EXCHANGE CAPACITY (CEC) is a very important index of the ability of a clay to hold onto cations released by weathering processes into the soil solutions. This is important in soils and for cleansing groundwater contamination.

hydrogen bonds The clays are held together by hydrogen bonds between the layers.

xxx 4M +++

Plants need to get ~20 different elements from the soils - the BIG FOUR and the other minor and trace elements. The BIG FOUR are needed in LARGE amounts: Nitrogen, Phosphorus, Potassium & Sulfur Minor elements are needed in smaller amounts, but are nonetheless essential: e.g., iron, magnesium, calcium Trace elements are needed in minute quantities - ppm or even ppb: e.g., copper, zinc, cobalt, boron, manganese, etc.

The BIG FOUR:

Artichokes, asparagus and rhubarb are among the very few perennial vegetables.

Sulfur 4. Sulfur (S)

Examples of NEEDLE ICE Effects of ice shattering on bricks in Waterville, Maine

How ice-wedging works to break up rocks

Ice-wedging damage to concrete supports for steps outside the Mudd Building and ice-wedging debris near the summit of Katahdin (right). All this at Katahdin has happened in the past 20,000 years.

2. Root Wedging The question always is, which came first, the roots or the fractures?

3. Salt wedging and Salt Hydration Cleopatra's Needle, in Central Park, New York City, showing progressive loss of detail with time as a result of hydration of salts in the rock. First photo is from ca. 1879…. 1930s1950s1980s

Olivia will tell us how this comes about...

Honeycomb weathering in Bishop Tuff, eastern California

4. Thermal expansion (from fires) In 2015, over 13 MILLION acres of western U. S. forests were burned. That's >24,400 square miles, or 52,300 square km! (= about 2/3 the total area of Maine!)

ONLY the outside few cm of the rock normally are affected. This commonly produces SPALLING.

5. Exfoliation - from surface unloading

Mass Wasting: It's not just in Cotter Union on Friday Night! Oso, Washington – 22 March, homes buried 43 people killed

In order to have mass movements, you have to have a MASS that is capable of MOVING! This means we're talking about SLOPES. Most of the land surface of the Earth has SOME slope to it – very few places are absolutely, perfectly flat.

SLOPE ANGLES are critical to this process (see figure at left). The steeper the slope, the more likely materials on it are to fail, and to slide or otherwise move downslope.

slope surface expands   the slope a. slope surface expands   the slope b. when the slope dries or thaws, gravity pulls directly DOWN c. HOWEVER, due to internal cohesion, the resultant is not quite as far downslope. Nonetheless,. Nonetheless, the net movement after each cycle is DOWN the slope.

2008 If you drive U. S. Route 2 across New Hampshire, you may see this lovely sight on a hillside above the roadway, between Gorham and Jefferson – the result of freeze-thaw-induced creep.

2013

Even a gradual slope can achieve this end – I go by these poles in Benton every day coming to and from campus. The Kennebec River is behind the trees at the rear of this lawn and field. The hill in the background is in Fairfield.

19 April, May, 2003

1983 And again in NOTE how the scar has healed from the earlier shallow failure. And yet again in Surface creep here is the product of expandable 2:1 clays, not freeze-thaw activity.

On a hillside outside Quito, Ecuador – again, a product of expandable 2:1 clays.

NEXT: more dramatic mass wasting Landslide in Ste. Jude, Québec, 2010; 4 people died when this event destroyed their home.