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Davies' Lectures
Broken Rocks, Rivers
56
Geology
Undergraduate 3
05/21/2015

Additional Geology Flashcards

 


 

Cards

Term
what are the qualities of rocks broken during tectonic uplift, exhumation, distortion?
Definition
the qualities of rocks broken during uplift, tectonic distortion, and exhumation is that they are broken at large-scale but intact down to silt size
Term
describe rocks broken during surface mass movements/faulting
Definition
rocks broken during surface mass movement or faulting can range from small boulder to nanometer size. it depends on stress and strain. large landslides often generate a lot of fine debris
Term
the two ways rocks can break
Definition
the two ways rocks can break is collapse, or dynamic fragmentation
Term
what is the strain/stress conditions related to rock breaking via collapse? what about the KE it produces?
Definition
rock collapse occurs under relatively low stress/strain, and produces relatively little KE. KE from breaking rocks is the fragements flying out at high velocity
Term

describe the process of dynamic fragmentation

 

Definition

the process of dynamic fragmentation

1. first, a rock particle is put under high stress by a landslide or fault

2. the stress deforms the particle. this deformation causes the particle to store elastic strain energy

3. when the stress reaches the elastic limit of the rock, denoted as Q, internal failure surfaces form. this releases the strain energy, and then the bits of the particle return to thier original shapes

4. the rock explodes, high KE because bits are moving fast. magnitude of dispersive stress = Q/3

Term
dominant size of mass movement: over long time periods, which tends to move more sediment: large landslides or small landslides?
Definition
dominant size of mass movement: over long time periods, large landslides tend to move more sediment than small landslides.
Term
most of the broken rocks on/in the ground were put there by landslides. what size landslide most likely put that broken rock there, knowing nothing else?
Definition
the dominant form of mass movement for broken rocks is large landslides. even though large landslides are less frequenct than small ones, they move enough mass to compensate
Term
what is the difference between loose granular flow and dense granular flow?
Definition
the difference between loose granular flow and dense granular flow is that dense granular flow is under a high confining pressure that packs the grains together
Term
both dense and loose granular flows involve distinct releases of energy that has built up
Definition
in loose granular flow, energy built up is released as fragment kenetic energy when grains break. in dense granular flow, energy is released as transient elastic strain energy and travels through the grains as P and S waves
Term
what is transient elastic strain energy?
Definition
transient elastic strain energy is how dense granular flows release built up energy. the energy propogates through the grains as a wave
Term
what is an example of a dense granular flow in nature?
Definition
a rock avalanche is an example of naturally occuring dense granular flow
Term
affect of rockfalls on glaciers
Definition
the affect of rockfalls on glaciers is that when rocks cover the top of a retreating glacier and stop melting, the glacier reverses it's retreat and starts to move forward, leaving a moraine
Term
when rockfalls trigger glaciers advances, what often goes makes up the moraine the glaciers make?
Definition
A rockfall triggers glacier advance. The moraine formed consists of rockfall debris
Term
ablation moraine
Definition
ablation moraine is a moriane caused by rockfall. Rockfall causes reflection of sun's energy, which is ablation
Term
ablation moraines have no ______significance
Definition
ablation moraines aren't connected to our climate history, they have no paleoclimatic significance
Term
how do we test if moraines are paleoclimatic or ablation-related?
Definition
we can test the cause of moraines by testing the sediment
Term
what do we look at in moraine sediment to see if they are paleoclimatic or ablation?
Definition
to see what caused a moraine, we focus on it's microsedimentology 
Term
debris from large landslides has grain size down to ____ and forms ____
Definition
debris from large landslides has grains on nanometer scale. large landslides like to form agglometerates
Term
the key to understanding the sediment balance between tectonic uplift and erosion
Definition
the sediment balance between tectonic uplift and erosion is that tectonic uplift-erosion=Δ land height. Davies teaches that these two things happen at the same rate, so change to land height is zero
Term

after earthquakes and landslides, the shape of a river may change, and this could affect the coast. How? (multiple step process)

 

Definition

how earthquakes and landslides changing river path affect the coast: 

1. earthquakes/landslides dump sediment into river's path, disrupting it's filuvially-optimal path.

2. as the river gets back it's it's optimal path, it erodes the dumped sediment downshore

3. the sediment is dumped at the coast, the coast progrades 

Term

relationship between slope steepness and sediment storage:

 

Definition
the relationship between slope steepness and sediment storage is that when a slope is steep we say it has little sediment storage
Term
four independent variables that determine river morphology
Definition

four independent variables that determine river morphology 

1. sediment supply, which is defined by the amount of tectonic uplift

2. rainfall

3. geology

4. base level i.e. the coast

Term
when they used stopbanks to cut the Waiho river off from 70% of it's fanhead, what happened?
Definition
when the Wahio was cut off from 70% of it's fanhead by stopbanks, it aggraded and steepened to be able to transport the same amount of sediment it could before
Term
takeaway from Kowhai and Hapuku river lesson
Definition
the takeaway from the Kowhai and Hapuku rivers unit was that sea level rise can mean aggredation or incision depending on the state of the river
Term
when europeans first came to NZ, they brought thier european river management with them. why didn't it work so well in NZ?
Definition
when europeans came to NZ, they they brought the idea of using stopbanks to control rivers. this works ok when tectonic uplift is slow, and rivers bring less sediment (remember, the sediment that comes down = tectonic uplift). NZ rivers carry enough sediment to overwhlem stopbanks
Term
how does the amount of sediment rivers carry relate to how they overwhlem stopbanks?
Definition
one of the ways rivers overwhelm stopbanks is aggradation. they build up so much sediment that they overflow during floods
Term
how are low land values connected to river management?
Definition
the higher value the land, the more money you have to protect it. in other countries, they can afford cement stopbanks. in NZ, there simply aren't enough people for that level of infrastructure. so we have gravel stopbanks
Term
tectonic uplift and erosion are in a dynamic equilibrium that stays at steady state, except for infrequent, short-term variations. what are these?
Definition
the steady state is interrupted by earthquakes that can cause erosion of 30 years worth of sediment in a short time
Term
when you alter a river, you reduce it's _____
Definition
when you alter a river, you reduce it's ability to carry sediment. This is called the bedload capacity
Term
Kosi Fan, India. Case study of what?
Definition
Kosi Fan, India is an example of river management gone wrong. they tried to put control banks on a river coming out of the himalayas, it aggraded and displaced 3 million people in 2 weeks
Term
what did they do in the lab to confirm the theory that the stopbanks were causing aggradation on the Waiho?
Definition
to test the theory that stopbanks were causing aggradation of the waiho, they built a microscale model of the river and added and took away stopbanks at will. doing this confirmed the theory
Term
Hermitage village is an example of what phenomenom?
Definition
Hermitage village was built in an area with flood control measures. Doing this restored the risk. this is a great example of how trying to reduce vulnerability can be a rat race because it encourages people to build more
Term
the NZ flood risk process standard says what?
Definition
the NZ flood risk process standard says that we need to understand the way that our river management is going to affect river path. we also need to understand the geomorphology that makes the river the way it is
Term
sustainable river management means doing what after you build stopbanks?
Definition
to sustainably bottle up a river with stopbanks, you must manually remove the sediment being built up and put it back in downstream
Term

global change on floods risk. explain

1. climate change

2. societal 

Definition

global change and flood risk

1. it's really hard to predict how global climate change will affect river management. 

2. it's really easy to see how societal change can/will affect river management. population growth, and the development that comes with it, will increase flood risk 

Term
what do we need to improve on with flood management laws in NZ?
Definition
flood management laws have a good start with the NZ managing flood risk process standard. but, it won't do much until that kinds of rules get into lower-level nitty-gritty regulations
Term
are slopes initiated or modified?
Definition
slopes don't start flat. they are modified, not initiated
Term

2 slope modifacation processes 

 

Definition

2 slope modifacation processes

1. weathering

2. denudation

Term
what does it mean for a process affecting a slope to be endogenic?
Definition

processes affecting a slope that are endogenic don't come from an external source. they come from the slope itself.

Endogenic processes don't move slopes, they just make them less steep 

Term
what does it mean for a process affecting a slope to be exogenic?
Definition
to say a process affecting a slope is exogenic is to say it comes from an external source. some examples are rivers, and coastal erosion. exogenic processes can move slopes around, unlike endogenic processes
Term

4 processes that weather rock

 

Definition

4 processes that weather rock 

1. freeze-thaw

2. plant roots

3. chemistry

4. stress 

Term
what is denudation in the context of slope processes?
Definition
denudation when we talk about coast processes is stuff sliding or flowing down a hill
Term
denudation can occur two ways
Definition
deundation can occur via stuff sliding or flowing down the hill
Term
mass movement stability: slope failure occurs along ____ path
Definition
slope failure occurs along a circular path. like a cycle wheel with a weight on it
Term
two ways to increase factor of saftey of a slope that we talked about.
Definition

the two ways to increase the factor of saftey of a slope that we talked about is 

1. take out moisture to increase friction via soil drainage

2. restribute mass from top to bottom. this is only really an option for slopes we have built

Term
what's the hard part about finding the factor of safety for a slope?
Definition
the hard part about finding factor of safety for a slope is finding frictional force, and the radius of the circular path you think it will fail along
Term
debris flow
Definition
when rockfall of 90% rock acts like a fluid
Term
stability analysis versus post-motion failure anaylsis
Definition

stability analysis is using the factor of safety to figure out if the slope is gonna fall. 

Post-failure motion analysis tells us how the motion continues and where it will stop 

Term
why was the landslide on to black rapids glacier an interesting treaching point for post-failure motion analysis?
Definition
the landslide on to the black rapids glacier was cool because the ice has a low coefficient of friciton, so the debris was going all over the place
Term
slopes fail when? (from a physics perspective)
Definition
slopes fail when gravity exceeds frictional force 
Term
what's the tool associated with post-failure motion anaylsis?
Definition
post-failure motion analysis usually involves modeling the expected landslide
Term
what do we call examining the way landslides move?
Definition
examining the way landslides move falls under post-failure motion analysis
Term
once we have figured out the liklihood and characteristics of possible landslides, we move to using that information to reduce risk. what are the two strategies for this?
Definition

the two ways to use information on landslide hazard to reduce risk:

1. create a number of landslides scenarios where proposed or existing human development would be affected

2. develop of landslide probability distribution to see the big picture. once you see the big picture, it is easier to rationalize what risks must be accepted and which must be changed  

Term
what's the biggest issue with hard engineering ways to stop landslides?
Definition
the problem with hard engineering ways to stop landslides is that when the landslides to inevitably come, they will be bigger and more destructive
Term
tree-domimated hillsides vs grass-dominated hillsides: difference in makeup and landslides
Definition
the soil under tree-dominated hillslopes is deeper. landslides from tree-dominated hillslopes are less frequent, but are larger
Term
my house is at the bottom of a landslide prone grass-covered hill. I want to plant some trees on it. what are 3
Definition

when considering the switch to trees to put off landslides, consider the following:

1. what is the difference between soil depth under grass and soil depth under trees? by planting trees, how much soil am I "adding"

2. how long will the transition take?

3. is bedrock weathered to soil at the same rate under grass and trees? what is this rate?

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