Thursday March 25th, 1999

Announcements: Exam is Thursday April 1st.

Lecture notes:

I. Preview
    A. Glaciers--mass of snow or ice that deforms and moves; glacial ice can be extremely thick or not thick at all
        1. Erosion of glaciers--occurs in two ways
                a. Freezing and thawing
                b. The flow of ice itself

        2. Transport of glaciers--occurs either in or on the glacier

        3. Deposition of glaciers

    B. Plastic flow/creep--the way a glacier moves

    C. Temperature greater than or equal to 0.8 Tmelt (temperature glacier melts)

II. Erosion and transport
    A. When we talk about glacial erosion or transport we mean mechanical weathering only
        1. Freeze-thaw--seep into cracks, freeze then expand
        2. Cold

    B. Not chemical weathering which is a mineralogical change from primary to clay
        1. Involves the release of cations (K, Na, Ca, Mg)
        2. Si to rivers then to the sea

II. Plastic flow/creep (Temperature greater than or equal to 0.8 Tmelt (80% melting temperature)
    A. The glaciers are close to their melting temperatures therefore we think that the glacier is "hot"

    B. Glaciers are in a "hot" environment like the asthenosphere

    C. Glaciers move in the direction that the surface slopes (usually downhill)

    D. "All glaciers deform internally, like slow pancake batter spreading on a griddle" (Alley 82).

    E. The weight of the glacier makes it move; large masses "want" to move downhill

    F. Glaciers are always moving--2 types respond
        1. Downhill
        2. Surface slope

III. Two (2) types of glaciers
    A. Major continental ice sheets (ex. Antartica)--most of their erosion occurs by "scouring out"; striations (scratches)
    in long grooves of rock; may be miles thick
 

    B. Alpine glaciers--these are more common to see; individual tops of mountains that have enough ice and snow to
    form a glacier

IV. Miscellaneous
    A. Paternoster--long, narrow lakes, or whole strings of lakes like beads on the string of the river connecting the
    glaciers, lie along the valleys

    B. Glacial advance--covering more ground than it used to

    C. Glacial retreat--covering less ground that it used to

    D. Everywhere you go in the world you can see glacial deposits and areas of glacial activity

    E. Glaciers have their first fracture within its top 60 meters

    F. "Calving" of a glacier--occurs when a glacier permeates in a body of water (warmer); this generates ice bergs