Geology 1010 Exam 2

What is the most common type of rock on Earth?

- sedimentary

What are some results/sources of sedimentary rock?

- landslides
- fossils
- crops
- agriculture
- oil

Parent Rock (sedimentary)

- starting rock
- acted on by weather

Steps of Forming a Sedimentary Rock

1. Weathering
2. Erosion
3. Deposition
4. Lithification

Weathering

- first step in sedimentary process
- breakdown of parent rock into sediment

Physical Weathering

- physically (w/ force) breaking down a rock
ex: plant roots (tree uprooting)

Frost Wedging

Type of Physical Weathering in which water enters cracks of rocks, freezes, and expands. This causes the cracks to become wider

Pot holes are an example of...

- Physical Weathering

Chemical Weathering

- chemical reaction, happens when minerals are unstable at certain temps/pressures
**more common
ex: quartz is more stable @ surface so won't react at surface,
-olivene is stable @ high temps&pressures so will react at earth's surface

Saprolite Formation

- rock that is so chemically weathered it is falling apart (crumbly)
ex: Feldspar + water + Carbonic Acid = Kaolinite (clay) is common in SC bc wet, humid environment

Oxidation

Atmospheric oxygen accepts electrons from other elements

Erosion

- second step in sedimentary process
- requires energy
- erosion is not weathering

What are the four types of energy? (erosion)

1. Water
2. Wind
3. Gravity (landslides)
4. Glaciers (picks up sediment and carries it)

Deposition

- third step in sedimentary process
- sediments, soil and rocks are added to a landform, building layers of sediment
-Deposited

Basin

- any place sediment can be deposited (can be as small as a pothole, as large as the ocean)

Accommodation Space

- the amount of space available in a basin to hold sediment

Subsidence

- in large basins, area can sink which allows for more accommodation space
** this is a constant cycle of sinking & filling until it has reached a max

Layers

- aka strata, beds
- deposition happens in layers

Lithification

- fourth step in sedimentary process
- making something solid
** important for stability

Compaction

- squeezing of sediment by adding more layers of sediment

Cementation

- natural cement that holds layers together
- comes from water that gets squeezed out of layers
ex: water is not pure H2O, dissolved substances aren't squeezed out (this is the cement)

Detrital Sediment

- aka clastic
- particles produced by physical weathering
Classified by grain size!!!! using common terms. Ex: gravel, sand, clay, etc

Size Class

- based on grain size

Traits of Detrital Material

- sorting
- rounding

Sorting

- are sizes uniform or different

Well Sorted

- sediment is consistent in grain size

Grain Sizes

- from large to small: gravel, sand, silt, clay

Moderately Sorted

- somewhat consistent in grain size

Poorly Sorted

- not consistent in grain size

The Better the Sorting

the more eroded it has been

Roundness

- measures how spherical the grains are

Poorly Rounded

- angular, sharp

Moderately Rounded

- somewhat rounded

Well Rounded

- very rounded

The More Rounded it is the

The Longer its been in transport

What is key in ID-ing clastic sedimentary rock names?

- grain size is key
ex: sand = sandstone
ex: silt = siltstone

Rocks with Gravel sized grains

Conglomerate (if gravels are moderate rounded)
Breccia (if gravels are poorly rounded)

Rocks with Sand sized grains

Sandstone

Rocks with Silt sized grains

Siltstone

Rocks with Clay sized grains

Shale (if layered)
Mudstone (if unlayered)

Chemical Sediments

- form from chemical weathering (dissolution & re-precipitation, saltwater evaporation)
- usually compromised of 1 major mineral type (ex: halite = rocksalt, quartz = chert)
- economically viable (b/c almost completely uniform of 1 mineral)
-SORTING AND ROUNDING DON'T APPLY TO CHEMICAL SEDIMENTS

Biogenic Sediments

- formed from biological activity (animals, plants)
ex: seashell
- some plants will not decay and make rock instead

Biogenic Rock Types/Names

- chalk = tiny shell remains
- limestone = carbonate particles
- coal = plant material
(all effervesce with HCl b/c carbonate is biogenic and reacts with HCl)

Mass Wasting

- landslides
- Transport of sediment and association materials downhill via gravity

Why are landslides important?

- is a sedimentary process (erosion using gravity), hazardous

Slope Stability

- processes that occur that cause a landslide

Angle of Repose

- max angle of steepness to still be stable
-CAN VARY A LOT DEPENDING ON OTHER FACTORS

Moisture Level

- if no moisture, dry particles will not interact and stick well so sediments will roll down easily
- If too much moisture, sediment turns into mud & flows downhill easily
- Moderate amount of moisture, adds cohesive force that holds grains in place

Amount of vegetation

- Little Vegetation, roots not holding well
- lots of vegetation, too many roots breaking up that suck out moisture, and add lots of weight to the slope
- moderate amount of vegetation, can help hold sediments together and flow water deeper into the slope and saturate it

What are the types of mass wasting?

- based on type
1. type of material moving
2. type of movement

Important Mass Wasting

-Rockfall
-Rockslides
-Mudslides
-Mudflows
-Snow avalanches
-Creeps

Rock Fall

-Material: Rock
-Movement: fell straight down
- falls move very fast, but stop once they hit the ground

Rock Slides

-Material: Rock
- Movement: Sliding Downhill
- Move slower due to friction, but they can conver long distances

Creep

-gradual downhill movement of sediments due to gravity

What causes mass wasting?

- EARTHQUAKES pushing unstable slope
- OVER-SATURATION- sudden addition of lots of waste (thunderstorm)
-ANTHROPOGENIC (man-made triggers):
1. poor landscape construction of a slope (intentional construction)
2. removing vegetation (trees) holding slope together

True or false: Unstable slopes do not automatically have a landslide occur.

True
- takes time for landslide to occur

Rick Assessment Maps (landslides)

- constantly updated, conditions can change in a matter of months

Prevention of Landslides

- drainage control
- decreasing slope grades
- building codes
- retaining walls
- rock bolts

Drainage Control

- wells, pumps, drains to take care of excessive moisture

Retaining Walls

- catches anything rolling from a landslide

Rock Bolts

- "nailing" sheet rock to bodies of rock

Is it expensive to prevent landslides?

- yes, but damage is more costly (~$10,000-$20,000 per $1 spent)

What is the case study example talked about in class that supports why its worth it to prevent landslides rather than wait for it to occur?

- Thistle, UT
- 1983 slide caused $200 million in damage
- was preventable IF $0.5 million had been spent on a drainage system

Geology in the News- hot spot activity

New study that hot spot activity in some areas is slower than previously thought

Why do we care about metamorphism?

- good for geological history

What causes metamorphism?

- made form increasing temperatures or pressures
(gets rid of old minerals, replaced with new)

Geothermal Gradient

- how quickly a temperature increases with depth (below surface)
- varies with location

What is the average geothermal gradient?

- 30 degC/km (if you were to drill a hole 1 km anywhere on the earth)
- Typical range: 20-60 degC/km
ex: high - 200 degC/km
low - 10 degC/km

When you are close to a subduction zone, what is the geothermal gradient?

- geothermal gradient is low
- need to go very deep before getting to a hot temperature

Contact Metamorphism Change

-magma comes in contact with rocks. make them become metamorphic
-solely driven by temperature
-LOCALIZED
rock is a good insulator for heat
effects small scale geographically
(metamorphism via heat)

What is pressure measured in?

- pascals or bars

What is a bar equal to?

- 1 bar = atmospheric pressure at surface
*works with metric system (kilobars, centibars)

Pressure Gradient

- ~300 bar/km depth
*(little) variation in location

Confining Pressure

- squeezing or applying pressure evenly from every direction
*think of a cube

Directed Pressure

- *aka differential stress*
- pressure from ONE direction

How do metamorphic rocks get back to the surface?

- Faults push rocks up and overtime through weathering, metamorphic rocks are exposed

Regional Metamorphism

- metamorphism via pressure
- large scale (east or west coast would experience at a time)
- caused by plate collision
-common places: subduction zone

Fault Metamorphism

- metamorphism via pressure
- trying to grind past each other
- localized (not large scale)
- pressure change
- very close and direct to fault

Metasomatism

- metamorphism via fluid
- present of fluid changes rock (not metamorphism)
- deep below surface
- VERY hot water flows through cracks, breaks down and dissolves minerals
- fluid can precipitate new minerals
- ores

Ores

- any deposit w/ high concentration of something valuable
(forms from Metasomatism)

Seafloor Metamorphism

- metamorphism via fluid
- ocean floor (typically near MOR), very cold seawater (iron-rich) at ocean floor flows into hot rock to change it into Metamorphic Rock
- when this happens to Basalt, rock changes from black to green

What does the type of metamorphic rock forming depend on?

- depends on parent rock's composition

Metamorphic Grade

- how much T/P changed
- low, intermediate, high
(Diagenesis is before low grade)
- ALL CHANGES OCCUR IN THE SOLID STATE ONLY!

Diagenesis Metamorphic Grade

- VERY low metamorphic grade, little change

Low Metamorphic Grade

- not much of a change

Intermediate Metamorphic Change

- more significant change

High Metamorphic Change

- complete change

What happens when there is too much change in metamorphic change?

- melting into igneous
***this is wrong

Index Mineral

- mineral that forms under a narrower range of pressure and temperature conditions
-Chlorite- low grade only
- Garnet- Intermediate Grade mostly
- Sillimanite- High Grade only

Metamorphic Facies

- *group of index minerals that form at ~ the same T/P*
ex:BLUE SCHIST FACIES- includes mineral glaucophane, lawsonite, epidote

What does facies information provide about metamorphism?

- reconstructs HOW metamorphism occurred
ex: contact metamorphism

Blue schist

- forms in subduction zones
- high pressure
- low temperature
(b/c it is on continent plate that moves over oceanic plate and used to be part of the seafloor (very cold))

Prograde

- when temperature and/or pressure is increasing
(rock is still getting buried deeper)

Retrograde

- both T and P are decreasing
(rock is getting closer to surface)

What can the length of metamorphism say about a mineral?

- changes within a mineral can record P/T changes (changes of 1 crystal in an index mineral)
ex: layers of crystals get older as you get closer to the center, layers show T/P conditions and time at each condition

What are the types of metamorphic rock?

- Foliated
- Non-Foliated

Foliated Metamorphic Rocks

- means "layers"
- minerals are lined up in layers
- *form by directed pressure*
ex: Slate - small crystals, foliated
ex: Schist - foliated, bigger crystals, hard to ID b/c crystals can over shadow layers
ex: Gneiss - minerals typically foliate by color (felsic/mafic pattern)

Non-Foliated Metamorphic Rocks

- no layered structure ("boring")
- *form by confined pressure*
- ID: made of mostly 1 mineral (hardness, effervescence, etc.)
ex: Hornfels - contains mostly hornblend
ex: Quartzite - mostly quartz
ex: Marble - mostly calcite (*effervesces)

Geology in the News: New Volcano on island could cause potential eruption

35,000 evacuation BALI as MOUNT AGUNG shows warning signs of an upcomin eruption

What is structural geology?

- the study of how rocks get deformed