E138 Weathering and Erosion

What is weathering?

process that turns bedrock into smaller pieces (sediment), chemical or physical

What is erosion?

transport of the sediment caused by weathering (can be from wind, water, gravity, or ice)

What is mechanical weathering? Example?

physical breakup of rocks

Examples: frost wedging, root wedging, biological activity

What is chemical weathering? Example?

chemical reactions that breakup or dissolve minerals and rocks

Examples: Dissolution (acidic water) and oxidation (iron oxide)

What is the water cycle?

circulation of water in the Earth’s atmosphere and through pools/stores

1. evaporation

2. transpiration

3. condensation

4. precipitation

5. runoff

What drives the water cycle?

solar energy (heats up water → evaporation)

Where is most of the water in the water cycle stored?

oceans (~97%) and glaciers (~3%)

How do you calculate discharge of a river? Q = (v)(A)

Discharge (Q) = velocity (v) x area (A)

What is a hydrograph?

shows how river discharge changes through time

What effects does Glen Canyon Dam have on the sediment and water in the downstream Colorado River?

• decreases discharge in the river

• reduced sediment supply to upper Marble Canyon by ~95%

• loss of sandbars (fewer/smaller camping beaches)

• experiment controlled floods are being released to re-establish sand bars

How do caves form? What rocks are required and what general chemical reactions occur? Chemical or mechanical weathering?

• develop when groundwater dissolves limestone

• CO2 reacts with H2O to form carbonic acid

• chemical weathering (dissolution)

What is groundwater?

• water that resides underground

• mostly in subsurface pore spaces

What are pores and porosity? Types of porosity?

• open spaces between sediments or crystal grains in soil or rock

• total volume of open space is termed porosity

  • primary (formed with the rock) and secondary (develops after rock has formed)

How does groundwater and porosity relate to caves?

• groundwater dissolves the limestone forming pores

• caves are a form of secondary porosity

What are some examples of dissolution features in karst landscapes?

disappearing streams, natural bridges, caves, sinkholes, springs

What are some solution features in caves? Why should people not touch them?

speleothems: stalactites (top down), stalagmites (bottom up), columns (other two connect)

• shouldn’t touch because oil from hands can cause them to stop forming

What surface features are present in a karst landscape?

sinkholes → funnel shaped features that result from roof collapse of caves

chemical weathering enlarges cracks in limestone

What does a sinkhole look like on a topographic map?

• closed, circular/oval-shaped contour lines

• identified by hachure marks (small, short tick lines pointing inward)

• usually in clusters within karst landscapes

What is the difference between an arch and a natural bridge?

• arches DO NOT involve flowing water

• natural bridge is carved by flowing water

Are arches an example of mechanical weathering, chemical weathering, and/or erosion?

all 3!!!

What are the 4 stages of arch formation?

• stage 1: vertical parallel fractures formed during uplift of the Colorado Plateau

• stage 2: spheroidal weathering widens fractures causing narrow fins to form

• stage 3: ice wedging and exfoliation weather the base of fins

• stage 4: water (dissolution) and frost continue to enlarge the holes (wind slowly smooths and widens the arches)

be able to identify these on a diagram!

What is differential erosion?

different rock types are stronger/weaker so they erode differently

How does differential erosion relate to waterfalls in layered stratigraphy?

differential erosion, caused by differences in rock strength, result in a waterfall