Exam 3 Flashcards
How old is Earth?
4,650 million years old
What lets you age and specifically date rocks?
radioactivity
Who was the father of geology and what did he do?
James Hutton
- thought Earth might be infinite
- led to a profound change in how geologist thought about things
What is a geological doctrine that changes in the earth’s crust have in the past been brought about suddenly by physical forces operating in ways that cannot be observed today?
catastrophism
What is a geological doctrine that processes acting in the same manner as at present and over long spans of time are sufficient to account for all current geological features and all past geological changes?
uniformitarianism
What is deep time?
Geological changes seem slow by human standards (processes require large amounts of time)
-Hutton noticed it in the rock record
What is an unconformity in which the strata below were tilted or folded before the unconformity developed; strata below the unconformity therefore have a different tilt than strata above?
angular unconformity
What is a type of unconformity at which sedimentary rocks overlie basement (older intrusive igneous rocks and/or metamorphic rocks)?
nonconformity
What is an unconformity parallel to the two sedimentary sequences it separates?
disconformity
Has Earth been through cycles?
Yes. The Earth has fone through many cycles of rock creation, uplift and deformation
What is the age of one geologic feature with respect to another?
relative age
What is the numerical age specified in years and what is it based on?
absolute age and it is based on radiometric dating
What is a recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region?
stratigraphic formation
What is a stratigraphic column?
A cross-section diagram of a sequence of strata summarizing information about the sequence/sequence of rocks divided into groups you can trace
What is the principle of cross-cutting relations?
If one geological feature cuts across another, the feature that has been cut is older.
What is the principle of superposition?
In a sequence of sedimentary rock layers, each layer must be younger than teh one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect
What is the principle inclusions?
A rock containing an inclusion (fragment of another rock) must be younger than the inclusion
What is it called when particular fossil assemblages can be found only in a limited interval of strata, not above or below this interval?
principle of fossil succession
What are elements with varying numbers of neutrons that have similar bases but different mass numbers?
isotopes
What is a stable isotope?
An isotope that never changes
What is a radioactive isotope?
An isotope that spontaneously decays
What is a half-life?
the time it takes for half of the element to decay (it is a characteristic of each isotope)
Explain the parent-daughter relationship when an element is decaying
As the parent disappears, the daughter grows in
What does an absolute age mean for igneous rocks?
Crystallization age is usually close to eruption/intrusion, but there may be some lag
What does an absolute age mean for sedimentary rocks?
A maximum age (Grains derived through erosion, not new)
- tricky to give exact dates
- more interested in where the sediment comes from
What does an absolute age mean for metamorphic rocks?
the last time mineral grain fell below closure temperature (age of last metamorphic event even if not a new material
What is a series of formations with similar lithologies or origins?
A stratigraphic group
How can you create a continuous geological column?
By correlating common periods of deposition in stratigraphic columns worldwide to fill in time gaps
What is a composite stratigraphic chart that represents the entirety of Earth’s history?
Geologic column
What was the cambrian explosion?
Large animals with more easily fossilized shells and skeletons
What are the key steps of fossil formation?
Sedimentary rocks, burial and mineralization
What depends on the speed of burial, chemical conditions, and presence of hard parts?
Preservation potential
Is the fossil record complete?
No
Does Earth want to be mountainous or flat?
Flat
Why isn’t the Earth flat?
Erosion occurs, but new land is also generated.
How are landscapes formed?
Lanscapes are formed by plate tectonics (uplift/subsidence) interacting with erosional processes (mostly water and ice)
What is the elevation difference between points on a landscape?
relief
What is the rate of change of elevation?
steepnesa
What do contour lines describe? And what are ‘V’ shapes in contours?
ridges, hills, slopes
The ‘V’ describe rivers, and they point upstream
What corresponds to the changes in strength of underlying basement rocks?
Changes in slope
What do valleys carved by water look like?
They have constant slopes and create V-shaped channels; produces a high density of smaller valleys
What do valleys carved by ice look like?
They have steep sides and flat bottoms U-shaped; produces a low density of big valleys
What is the triple point?
A place where water vapor, liquid and ice can all coexist on the surface of Earth
How does groundwater form?
Water collects as standing water or infiltrates to form groundwater
What is melt and groundwater discharge that eventually collects into streams?
Sheet wash
What forms due to feedback between erosion and topography acting on small differences in flow/strength of a substrate?
Channels
What are permanent streams?
Defined by water flowing all your abundant rain, groundwater discharge and low evaporation.
What are ephemeral streams?
Streams that do not flow all year due to low rainfall, low water table and high rates of evaporation.
What is a drainage network and how do they work?
Individual streams join and link together in drainage networks. As you go downstream, channels get bigger, focusing water collected from larger areas.
How does groundwater form?
Water collects as standing water or infiltrates to form groundwater
What is melt and groundwater discharge that eventually collects into streams?
Sheet wash
What forms due to feedback between erosion and topography acting on small differences in flow/strength of a substrate?
Channels
What are permanent streams?
Defined by water flowing all your abundant rain, groundwater discharge and low evaporation.
What are ephemeral streams?
Streams that do not flow all year due to low rainfall, low water table and high rates of evaporation.
What is a drainage network and how do they work?
Individual streams join and link together in drainage networks. As you go downstream, channels get bigger, focusing water collected from larger areas.
What is a branching or tree-like drainage pattern? Where is this common?
Dendritic; Common in regions of uniform material
What is a drainage pattern in which draining occurs in all directions away from a point? Where is it most common?
Radial; found at the perimeter of a high region or feature (mesa, peak, mountain, etc.)
What is a drainage pattern in which channels are aligned primarily in two directions? Where is it most common?
Rectangular; Common in gently sloping areas of orthogonally jointed rocks
What is a drainage pattern in which the trunk stream flows through resistant rocks and tributaries flow between ridges? Where is it most common?
Trellis; Common where surface alternates between erodible and resistant materials
What is a drainage pattern that has several streams with parallel courses? Where is it most common?
Parallel; Common on surfaces with uniform slope
What is the area of land that drains into a single stream?
A drainage basin or watershed
What are ridges and peaks that separate drainage basins?
Divides
What separates drainages that flow to different water bodies?
Continental divides
What happens when streams flow downhill?
They convert gravitational potential energy into kinetic energy, which can be used to erode and transport sediment
What is the ultimate energy source?
The Sun
What are three things flowing water can do?
1: Scour surfaces of existing sediment
2: Break and abrade rock (sandblasting; potholes)
3: Dissolve bedrock
What is composed of the larger particles that roll, slide and bounce along the bed of the channel (saltation)?
Bed load
What consists of ions from mineral weathering?
Dissolved load
What is made of fine particles entrained in the flow?
Suspended load
What changes with the current strength?
The suspended and bed loads carried by streams and rivers
What do you call the maximum load (coarse, fine and dissolved material) transported?
Capacity
What do you call the maximum grain size transported?
Competence
What are the conditions of headwater?
Gradient is steep, discharge is low, sediments are coarse, and the channel is steep and rocky
What are the conditions found at the mouth?
Gradient flattens, discharge increases, sediment grain sizes are smaller and channels develop broad meander belts
How do meanders evolve?
The continue to get more sinuous by cut bank erosion and point bar growth before eventually being chopped off
What is the highest velocity water that erodes the outside of a bend called?
Cut bank
What is the inside of the bend called?
Point bar (the site of sediment deposition)
What do you call a meander cut off by the main channel?
Oxbow lake
What happens at a delta?
Consist of sediments deposited at the mouth of a stream, when a stream enters standing water the current slows, loses competence and sediments drop out
What is the shape of a delta a function of?
Sediment supply and the competing strength of the river compared with the strength of ocean currents and waves that redistribute sediment off shore
What are three shapes of deltas?
A shaped
Arc-Like
Bird’s foot
How do rivers flow and what do slopes do?
Rivers flow from high to low elevation and slopes tend to flatten between source and mouth (concave)
What kind of materials do shallow and deep slopes carry?
Shallow slopes carry fine sediments, deeper slopes carry coarser materials
What are rapids caused by?
Turbulent flow of water
What do rapids reflect?
Rapid reflect steep gradient and or high friction
What causes rapids’ steep gradients and high friction?
Flow over bedrock steps (edges of resistant layers)
Flow over large clasts
Narrowing of a channel
Increase in gradient
When a channel narrows, does the water slow down or speed up? When it widens?
Speeds up/slows down
What are factors that cause waterfalls?
- Gradient is so steep that water cascades or free falls
- waterfalls scour a deep plunge pool
- basal erosion leads to collapse of overlying rocks
- waterfalls are temporary base levels
What do shallow slopes on flood plains allow?
Deposition of fluvial sediments/alluvium (finer grained further downstream) where energy drops (channel/point bars and as meander migrate)
What do you call many interfingering channels on the flood plain that form when the sediment load is very high?
Braided streams
What do rivers do with their sediments at the mouth?
Drop them, creating a delta, and causing the land to migrate out into the sea
Can deltas migrate to different locations?
Yes
What do you call the lowest elevation a stream’s surface can reach?
Base level
What happens if a base level rises?
Stream flow slows and the valley becomes filled with more sediment
What happens if a base level falls?
Stream flow quickens and the incision of channels may leave stranded terraces?
What are changes in base level caused by?
Tectonic uplift or changes in sea level
What marks former flood plains?
Stream terraces
What is the cause of most landscape changes?
Stream flow
What is it called when one stream captures the flow of another?
Stream piracy
What is a stream that flows across deformed terrain despite geologic structure (such as folds)?
Superposed streams*
What do you call streams that are caused by tectonic uplift raising a region that has an entrenched stream and erosion keeps pace with the uplift, so the stream remains in its channel?
Antecedent streams*
What do you call it when meanders are raised, resetting the base level and the meanders erode into the uplifted landscape?
Stream rejuvenation*
What causes floods?
Heavy rainstorms, rain on saturated ground, rapid snow melt, dam/levee failure
How of risks of floods specified?
In annual probabilities
Where is most of the Earth’s water, and how does it get there?
Most water percolates into the subsurface and is stored/transported as groundwater
What do you call water that is in pores and fractures in subsurface rocks and sediments?
Groundwater
What fields use groundwater?
Domestic, agricultural and industrial uses
What do you call unfilled voids in a rock or sediment?
Porosity
What are pores that are left over from deposition/formation?
Primary
What are pores left from dissolution or fracturing?
Secondary
What if porosity=0? 0.1?
0 means it is a solid rock
0.1 means 10% of it is air
What do you call how easily water can flow through a rock? What does it depend on?
Permeability; depends on pores being interconnected (A porous rock isn’t necessarily permeable)
Are soils permeable?
Yes. This is how groundwater gets there
What do you call the level where percolated water has completely filled (saturated) the available porosity?
Water table
In what regions is the water table close to the surface? In what regions some way beneath the surface?
In humid regions/in arid regions
Can the level of a water table change seasonally or due to long term climate change?
Yes
What allows storage or flow of groundwater?
Permeable aquifers
What impedes flow and has low storage capacities?
Impermeable aquitards
What kind of aquifer intersects/is exposed to the surface? Is it easily contaminated?
Unconfined; Yes
What kind of aquifer beneath an aquitard called? Is it susceptible to pollution?
Confined; Less susceptible to pollution
What is an aquifer perched on top of a localized aquitard? And what does it produce?
Perched; produces a water table closer to the surface (Higher than the regional level)
How does the water tables change due to topography?
Water table usually mirrors the topography with a lower relief (Because water flow is slow)
How far can groundwater travel? What does the transit depend on?
It may flow hundred of kilometers across sedimentary basins. The transit time depends on the flow path. Deeper flow paths take longer
Can we consume more groundwater than the Earth supplies?
Yes.
