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Lecture

GGR100H1 Lecture Notes - Tectonic Uplift, Spheroidal Weathering, Lithosphere


Department
Geography
Course Code
GGR100H1
Professor
Sarah Finkelstein

Page:
of 6
Lithosphere (March 1st, 3rd, 8th cover Lithosphere)
Lithosphere: the solid earth. What processes occur on the ground?
What shapes the Earths surface?
Endogenic processes: processes occurring inside Earth having to do with several
things such as geophysical movement of fluids, plate techtonics, formation of rocks,
tectonic uplift (creates mountain ranges/sea floor spreading). These happen very
slowly and are in traditional realm of geology.
Exogenic processes : things happening above surface/outside innards of earth.
>Geomorphology: process-based study of landforms (earth + shape).
-constant supply of raw materials that’re then worked
-dynamic equilibrium between uplift of tectonics and wearing down by weathering,
mass wasting and erosion (rock moved with an agent: water/wind/ice move rock)
The Rock Cycle
-2 diff. types of plates make up lithosphere: oceanic crust (heavier) and terrestrial
crust (hard brittle crust plate tectonics float atop molten, plastic asthenosphere).
>when these come into contact, interesting stuff happens
> plate tectonics: solid sea-floor gets subducted beneath land plates, then melts
> weathering, mass-wasting and erosion wear down solid rock that’s uplifted by the
rock cycle. No tectonic activity would mean earth would be totally flat plain, w/o
that uplift.
> molten rock underneath, brittle plates on top in asthenosphere
Weathering
-Higher, taller, more jagged ranges means newer mountains. Flatter, rounded and
low ranges mean older mountains. Rockies = newer vs. Appalachians = older.
-process wherein solid rock breaks down and forms smaller rocks, called regolith
(weathered rock).
-divide weathering into two forms, physical and chemical. These forms interact in
nature and can be observed working simultaneously.
Physical (mechanical) weathering: breakage, rocks disintegrate w/o chemical
alteration
>e.g. physical altering of rock; e.g. water freezes inside rock and breaks from inside
(frost-action)
Erosion
-weathered rock is subject to erosion
-refers to the transportation/removal of broken material by diff. forces;
>Agents of Erosion: wind, water, ice
-Bedrock w/weak areas due to gaps (JOINTS) where water can enter breaks into
regolith vegetation promotes weathering by worming into gaps (Biosphere &
lithosphere work together)
1).Frost action: role of joints; wedge-axn breakage e.g. Toronto road potholes by
frost-axn
2). Salt-crystal growth: in arid climates, expansion/crystallization of solutes left
Lithosphere (March 1st, 3rd, 8th cover Lithosphere)
behind by heightened evaporation promotes weathering. Salt-expansion grows
chemically.
3). “Unloading”: release of weight and pressure on a rock surface. Rock surface has
a lot of easily erodible material on top. Once all of it’s gone, rock below can ‘relax’
and spaces between the molecules of rock can expand, shedding rock in the
process of ‘relaxing’/expanding. As expansion goes on, pushes off upper layers of
rock in sheaths.
Chemical weathering: interaxns ‘tween air and water chng. rock chemically.
>e.g. water contains solutes that can be slightly acidic which can chng. rock
chemically
-Water = very potent agent of chemical weathering b/c it’s a solvent; propensity for
acidic solutes. Water is very good at slowly forcing change.
- Chemical weathering increases w/increased temp. + ppt.
1).Hydrolysis: chemical rxn w/water + carbonic acid
e.g. Feldspar weathers clay + sand. Water produces these new minerals from
Feldspar; over time breaks down granite (which contains Feldspar).
1.5) Hydration: water molecules come into the crystal structure/lattice of minerals,
changing the properties of the mineral so it can expand/be more susceptible to
other types of weathering (physical)
2). Oxidation: rxn of metals with oxygen
e.g. free oxygen in air takes e-s from elemental Fe in rocks & minerals; iron oxide
Iron oxide = softer thus more easily removed rust enhances oth. forms of
weathering (physical)
3).Carbonation/Dissolution: rxn with a weak acid; moisture in atmosphere w/carbon
dioxide. Dissolution of calcium carbonate & removal in solution.
e.g. Carbonation esp. good at removing carbonate-containing rock; Niagara
Escarpment.
> weak acid particularly good at dissolving rocks. Sedimentary rocks containing
carbonate such as those making up Niagara Escarpment (made out of ‘dolomite’),
and bedrock in Toronto.
Sources of acid: rain water, humic acids (weak yet effective for carbonation) in soils
(plant decomposition)
>Importance of soils for weathering: soils right @ interface where weathering taking
place in biosphere
Spheroidal weathering: chemical rxn with water falling as ppt. creates smooth,
rounded edges where water continuously falling over rocks (Niagara Escarpment)
-Ppt. vs. Temp. graph:
>wetter/hotter conditions = most chemical weathering. *physical can happen in
warm/dry places b/c of salt-crystal expansion, otherwise, graph is a good
representation of the general distribution of both types of weathering.
>Dryer/cooler = more frost-axn = most physical weathering.
Lithosphere (March 1st, 3rd, 8th cover Lithosphere)
Karst landscapes: explain caves, underground caverns etc. hollowed out by carbonic
acid that comes with rainfall/water
- Chemical weathering of surface and sub-surface limestone by carbonic acid
*role of ground water
-“Lost Rivers” – where streams create waterfalls underground/into underground and
hollow out caves
Karst surface features: Limestone “pavement” = “Karren”
>spheroidal weathering can happen with Karren situations
>rock has crystal structure, areas of physical weakness where the ‘joints’ (straight
lines that water enters) can enlarge these features in places like Kentucky, or
Niagara Falls.
>Karst identifiable on topographic maps by certain telling signs:
o no ‘surface streams’ (?) flowing from higher to lower areas
x sinkholes: small notches pointing inside depressions on contour lines, which says
relief going down into ground as opposed to up
Development of Karst
-big caves/caverns and warm conditions
-limestone CaCO3 is easiest rock to chemically weather and form Karst as opposed
to dolomites (harder to weather, more resistant)
-many joints (indicating places of weakness) more joints = more creation of
subsurface features from water introduction
-actively flowing groundwater/aeration. Karst can’t happen in, say, permafrost areas
b/c no movement of water
-vegetation: lots of this promotes chemical weathering by vegetational decay
creating conditions for it/creating acidic by-products. Some places with lots of
vegetation don’t necessarily form Karst.
Tower karst: Works well in moist tropics. 3 stages, slide shows time passing
(sinkholes form, get bigger, wear away, caverns form and streams disappear by
becoming lost rivers) and eventually towers formed out of worn away sinkhole
areas, these pinnacles left over from pattern of water flow, or slightly diff. mineral
composition in particular rocks leading to some features more susceptible to
weathering and some less susceptible (which stick around, becoming pinnacles).
>Tower karst happens in very old landscapes; former surface corresponds to top of
pinnacles
Mass Wasting and its Controlling Factors & Classes
-synonymous w/mass movement
Factors:
1).Slope angle: makes possible an interplay of gravity and friction, forces that’ll
allow material to roll down slope or not
> gravity removes material b/c material will always move down slopes
2).Type of material is important: Does the material absorb water well or not? e.g.
clay (absorbs water, can become runny and just flow down slope whereas non-