Ch 14, Weathering, Karst Landscapes, and Mass Movements

Question 1

Denudation:

Answer 1

process that wears away or rearranges landforms

Question 2

Dynamic equilibrium model

Answer 2

The balancing act between tectonic uplift and erosion, between the resistence of crust materials and the work of denudation processes.

Question 3

Geomorphic threshold

(Force overcomes resistance)

Answer 3

When a geomorphic system moves from the slow accumulation of small adjustments to a point of abrupt change that takes it to a new system state.

E.g. When a flood establishes a new river channel or a hillslope adjusts after a landslide

Question 4

For material to move down a slope it requires:

Answer 4

Friction, inertia, and cohesion of particles to one another

Frication > inertia

Question 5

Slope and stability

Answer 5

A slope is stable if its strength exceeds these denudation processes and unstable if its materials are weaker than these processes

Question 6

Weathering:

Answer 6

The process that breaks down rock at earth’s surface

Question 7

Physical weathering:

Answer 7

The disintegration of rock without any chemical alteration. By breaking up rock, physical weathering produces more surface area on which all weathering may operate

e.g. You break a rock, it crumbles on the table and takes up more surface area

Mainly caused by:

frost action
salt-crystal growth
exfoliation

Question 8

Bedrock, regolith, and soil on hills

Answer 8

Inner side of hills contain bedrock, but the upper/surface layer of bedrock is regolith which is exposed to weathering, and those post weathered materials get deposited and become a basis for soil development

Question 9

Factors which effect weathering processes:

Answer 9

1. Rock composition and structure (jointing)
2. Climatic conditions
3. Subsurface water
4. Slope orientation
5. Vegetation

Question 10

Frost wedging:

Answer 10

When water freezes it expands by 9%, so the repeated action of freezing and thawing water causes it to break rocks

Question 11

Salt crystal growth:

Answer 11

Common in arid climates, occurs when evaporation draws moisture to rock surfaces, leaving behind salt crystals that grow and break apart rock grains

Question 12

Exfoliation:

Answer 12

When rock’s outer layer peels; occurs from pressure so when the pressure is released from a granite pluton after the removal of overlying rock. As the weight is lifted, the granite expands and forms cracks, a process called pressure-release jointing

Question 13

Chemical weathering:

Answer 13

Chemical breakdown, always in the presence of water, of the constituent minerals in rock

Question 14

What are the types of chemical weathering

Answer 14

Spheroidal weathering: Chemical weathering that softens and rounds the sharp edges and corners of jointed rock (thus the name spheroidal) as water penetrates the joints and dissolves weaker minerals or cementing materials

Hydration (Hydrolysis): When water interacts with a rock’s minerals causing it to expand creating a wedging that stresses the rock forcing grains apart.

Oxidation: When certain metallic elements combine with oxygen to form oxides
E.g. Rusting of iron

Dissolution of carbonates: Water vapor dissolves carbon dioxide, causing a precipitation of carbonic acid, and this acid can dissolve many minerals like limestone

Question 15

Karst Topography:

Answer 15

A limestone region with a specific landscape of pitted, bumpy surface topography, poor drainage, and well developed solution channels underground,
due to chemical weathering

Question 16

Formation of karst:

Answer 16

1- The limestone formation must contain 80% or more calcium carbonate for dissolution processes to proceed effectively.

2- Complex patterns of joints in the otherwise impermeable limestone are needed for water to form routes to subsurface drainage channels.

3- An aerated (air-containing) zone must exist between the ground surface and the water table.

4- Vegetation cover is needed to supply varying amounts of organic acids that enhance the dissolution process

Question 17

Features of Karst landscapes:

Answer 17

Sinkholes: circular depressions in the ground surface caused by dissolution of limestone landscapes

Karst valley: continued
dissolution and collapse leading to sinkholes that coalesce to form a valley

Tropical Karst: A unique landscape found in tropical areas where rain and chemical weathering shape limestone rock, in star-shaped hollows called “cockpits” and cone-shaped hills between them

Question 18

Caves:

Answer 18

• Form in limestone (easily dissolved by carbonation)
• Form just beneath the water table

Question 19

Mass movements

Answer 19

The downslope movement of a body of material made up of soil, sediment, or rock propelled by the force of gravity.