Weathering

Question 1

what is weathering?

Answer 1

• Alteration of materials by atmosphere, water, animal and plant life, and temperature fluctuations
• Occurs at or near surface
• Involves mechanical breakdown (disintegration) and/or chemical breakdown (decomposition)

Question 2

mechanical weathering

Answer 2

• physical forces break rock into smaller pieces without changing rock’s mineral composition (no chemical change)
• Ie. Smashing with hammer
• Surface area is one of the most important factors -> mechanical weathering increases surface area -> increased surface area = increased weathering
• includes frost wedging, talus deposits, exfoliation/sheet jointing, root wedging, salt wedging, thermal heating and cooling

Question 3

chemical weathering

Answer 3

• chemical transformation of rock into one or more new compounds
• Produces either ions in solution or alternation minerals
• Happens a lot in hot, wet, humid tropical environments
• Processes that decompose rock by chemically altering the parent material
• includes oxidation, solution/dissolution, and hydration

Question 4

weathering process

Answer 4

• Weathered material is eroded and then transported by water, gravity, or wind, deposited as sediment
• Eventually forms sedimentary rocks
• Creates landforms; landscape development

Question 5

frost wedging

Answer 5

• mechanical weathering
• 9% volume expansion due to ice -> wedges rocks apart
• Common in cool, temperate climates

Question 6

talus deposits

Answer 6

• mechanical weathering

- Mechanically weathered fragments fall down slope due to gravity

Question 7

exfoliation (sheet jointing)

Answer 7

• mechanical weathering
• Due to pressure release in intrusive rock
• Removal of overburden (unloading) = decreased confining pressure
• Causes expansion of rocks and sheet jointing
• Ex. The Chief

Question 8

root wedging

Answer 8

• mechanical weathering

- tree roots grow in rock cracks and wedge them apart

Question 9

salt wedging

Answer 9

• mechanical weathering

- salt gets stuck in cracks and accumulates/grows, wedging rocks apart

Question 10

thermal heating and cooling

Answer 10

• mechanical weathering

- causes rocks to expand and contract, which expands cracks -> happens in areas with extreme weather swings

Question 11

oxidation

Answer 11

• chemical weathering
• Affects any material containing iron
• Result of development of earth’s biosphere

Question 12

solution/dissolution

Answer 12

• chemical weathering
• Co2 dissolves in rain, making it slightly acidic
• When it rains on calcite (limestone), calcite fizzes and begins to break apart
• Complete dissolution = no solids left
• Forms caves, caverns, stalagtites/stalagmites, and groundwater high in dissolved ions
• Forms Karst topographies

Question 13

hydration

Answer 13

• Most common chemical weathering process
• Acidic rainwater reacts with silica-rich rocks (feldspar) to form clays
• A new solid is left after weathering by “hydrating” feldspar -> clay mineral and a bunch of silica leftover

Question 14

susceptibility to weathering

Answer 14

• Some minerals are more susceptible than others (ie. Quartz less susceptible)
• Susceptibility to wearing is in reverse order of Bowen’s reaction series (ie. Quartz least suceptible, Olivine most susceptible) -> High P and T minerals are out of equilibrium with surface P and T conditions

Question 15

weathering products

Answer 15

• Reduction in size/dissolution (Ex. Mechanical weathering produces smaller fragments of rocks and minerals)
• Transportation: gravity/wind/water/biology
• Deposition
• Alteration minerals from chemical weathering (ie. Clays like Kaolinite -> product of feldspar weathering
  Porcelain, magazine paper, protein shake
• Clastic sedimentary grains: sand and salt (Quartz most common component since it’s the most resistant)
• Solutions: dissolved minerals and ions from chemical weathering (Can be precipitated elsewhere -> ex. Red sea -> minerals/ions precipitate out of it as it evaporates)
• Landscape development (ie. Grand Canyon)

Question 16

weathering and landscape development

Answer 16

• Numerous weathering processes and extensive erosion (“differential weathering”) over time produced the Grand Canyon
• Example of differential weathering: weak shale overlain by quartz-rich sandstone -> shale eroded, quartz-rich won’t
• Arches start as solid sandstone with cracks -> progress to fins of sandstone -> weaker rocks weather faster -> Some produced arches, some don’t -> depends on location of weaknesses -> All will eventually erode

Question 17

clastic sediments

Answer 17

eroded fragments of pre-existing rocks

Question 18

sediment grain size and shape

Answer 18

• indicates transport distance and energy/turbidity of environment
• small/fine, round grains have travelled farther
• large, sharp/angular clasts are close to where it eroded (clast = big grain)
• High energy environments : only coarse heavy material can be deposited – fine material remains in suspension (Ex. Rushing river)
• Low energy environments: fine material can settle out (Ex. swamp)

Question 19

different grain sizes

Answer 19

• Fine: Muds -> clay, silt (shale, mudstone, siltstone)
• Medium: Sand (sandstone)
• Large: Gravel -> pebble, cobble, boulder (breccia (angular particles), conglomerate (round particles))

Question 20

grain sorting

Answer 20

• Sorting refers to the distribution of grain sizes in sediment or sedimentary rock
• One way sediment is sorted is by running water -> The longer sediment travels, the more consistent the grain size (the better sorted it is)
• sediments close to source: large, angular grains; poorly sorted
• Sediments far from source: small, rounded grains; well-sorted

Question 21

alluvial fan

Answer 21

high area, flash floods happen and push sediments down the hill, results in angular shapes

Question 22

soil

Answer 22

• regolith that contains organic material and can support life
• Vital part of the earth system
• Proxy for rock types – mineral exploration “soil sampling” -> composition of soil changes depending on what rock is below it, as well as what minerals are it in
• Helped spread bisophere across surface of land -> lead to plants developing -> roots eroded rocks, drawing down C02 -> planet cooled down -> ice age -> glaciers and oceans froze -> ocean levels sank -> mass extinction of shallow water animals/organisms (ex. Corals)… we need some greenhouse gas to keep planet alive

Question 23

regolith

Answer 23

loose unconsolidated material that covers rocks

Question 24

which of the earth’s major systems do soils directly interact with?

Answer 24

• All of them!
• Geosphere (rock): mineral matter in soils is derived from rocks
• Atmosphere: weathering mineral material and organic material in soil will use various atmospheric gases including oxygen and carbon dioxide
• Hydrosphere: soils store water, making it available for plants
• Biosphere: soil is a medium that supports numerous microbes, animals, and plants