Geology - Exam 2

Do contour lines (on top map) every cross or end at a point?

No, they connect to the other end of the line in a circle

Closed loops are either:

Hilltops or bowls (low point in topo)

How do you find distance b/w the highest and lowest point through a topo map?

Relief between X&Y / Distance between X&Y

Vertical change between two points. You find by determining the difference between highest and lowest points in the map

What is relief in topographic maps? How do you find it?

**Tilted sedimentary rocks** – indicates that these have been deformed\*

Assume this is caused by plate tectonic activity

What is strain?

*deformation* of the rock caused by stress 

What is the first type of strain?

Brittle: rock fractures and breaks

What is the second type of strain?

Ductile: rock bends and flows

What temperature and pressure favor brittle deformation?

Brittle deformation favored where both T and P are low

**How far down in crust does this behavior change?**

In typical continental crust, rocks within 10-15 km of the surface behave in brittle fashion

**What does deformation produce?**

\
* Large scale – regional structures:
* Faults
* Due to brittle deformation
* Folds
* Due to ductile/plastic deformation 

Dip-slip faults

Motion is either up or down fault plane

Normal faults in areas where the crust is extending

Strike slip fault:

motion is sideways along fault plane

Where is the oldest rock in an anticline?

In the middle and younger is on top of it

Where is the oldest rock in an syncline?

Oldest beds on the outside, Youngest beds in the middle

What are some structures formed through deformation?

Faults and folds

Elements of folds

**Limbs**: planes on either side of the fold

**Interlimb** **angle**: tells you how it folds

**Axial plane**: marks the symmetry between the limbs

To geologists EQ =

slip on a fault

**Rocks break, releasing seismic energy**

Difference between P wave and S wave velocity is…

\~**2.5 km/second** (for close EQs)

When you feel the P wave hit, start counting…

* Stop when you feel the S wave
* Multiply seconds by 2.5 km

How do you calculate how long you have to get cover for earthquake

Distance away from location//2.5 km

How do tsunamis form?

1. Earthquake
2. Collapse of a volcano/volcanic eruption
3. submarine landslides
4. onshore landslides in which large volumes of debris fall into the water

Plate boundary reason for tsunami?

***Convergent plate margins produce “Megathrust” earthquakes along the subduction zone boundary***

what is superposition?

oldest rocks must be at the bottom

How are tsunamis generated?

As a thrust fault moves, the hanging wall is rapidly uplifted

A tsunami is caused by the lifted water column escaping laterally

Paleotsunami

You can tell the geological/oceanographic history of a place based on

Can reconstruct wave height, pre-wave water depth, and possible size of asteroid from these deposits

Salt water is….

more dense than freshwater

Cold water is…

more dense than freshwater

What are three ways that ocean currents are created?

* Controlled by heat transfer – controls global climate


* Surface – driven by wind
* Deep – driven by water mass density 

Air currents

Move from high = low pressure… this produces wind

Combination of Coriolis Effect and the vertical rotation of hot/cold air work together to form 3 sets of atmospheric convection cells

* Cells converge every \~30°

Coriolis Effect

As the wind blows across the surface of the water, the water is also deflected by the Coriolis Effect

* Decreasing speed with depth
* No movement \~100 m depth
* Net ocean current movement \~90° of wind direction


* Surface waters are deflected \~45°

**Ekman Transport**

What are eddies?

Circular movement of surface waters

Measurement of ocean depths (below sea level) and the charting of the shape of seafloor topography

**Bathymetry**

 a mass moving in a rotating system experiences a force (the *Coriolis force* ) acting perpendicular to the direction of motion and to the axis of rotation.

***Coriolis Effect***

DEEEP Water currents

Surface waters cool, become more dense, and sink

* Driven by temperature + salinity between water masses

***Thermohaline circulation***

What is downwelling?

where surface water is forced downwards, where it may deliver oxygen to deeper water

What is upwelling?

 a process in which deep, cold water rises toward the surface.

What is deep sea “pelagic” sediments made of?

Consist of clays, cherts, fine-grained calcite muds

What are deep sea cosmogenic sediments?

Microscopic spherules and meteorite debris from outer space

* Make up 10-30% of seafloor sediment!

Hydrogenous sediments?

Form metal-rich nodules on the seafloor from chemical reactions

* Rich in manganese – target for deep sea mining

Continental shelf

* Extends 70 km – 150 km (dependent on margin type)


* Flat (\~0.1°)


* Exposure dependent on climate

Continental slope

Where ocean basins begin 

* Steep topography (\~4°)

May contain canyons

* Ex: Monterey Canyon

**Lithogenic Sediments?**

Detrital fragments of pre-existing rocks

* May be from the continents or erupted from volcanoes

Variable size

* From fine-grained clays to coarse gravels

**What controls or affects coastal systems? Pt. 1**

\
* Sediment source/production
* Sediment transport:
*  Waves, tides, humans

What controls or affects coastal systems? Pt. 2

* Uplift – Tectonics and climate
* Sea level change – climate and humans

How do waves form?

Waves form as a result of consistent, strong winds blowing across an open stretch of water.

What factors into the size of waves?

1. wind velocity
2. wind duration
3. fetch – the distance over which the wind blows

What are waves like in the Zone of Generation?

irregular, chaotic, turbulent

What happens when waves disperse from the ZoG?

they stop interfering with each other and become orderly swells 

What happens when waves get closer to shore and interact with the sea floor?

* Causes friction and drag, slowing the motion at the bottom


* Motion of the top hasn’t changed, so the wave topples over

What depth must water be to begin interacting with the seafloor?

Occurs when water depth = ½ wavelength

What modifies the characteristics of a beach?

* amount of sediment supplied


* current, tide, and wave energy

Why do **tides** occur?

Tides result from the gravitational attraction of the sun and moon on the ocean

When do the highest high tides occur?

Highest high tide occurs when the sun and moon are aligned

When do the lowest high tides occur?

Lowest high tide is when the sun and moon are at right angles to each other

What are tidal ranges controlled by?

* ocean bottom topography


* perturbations in the lunar orbit
* tilting of the Earth’s axis

Barrier islands? Why do they exist?

Only occur in areas where tides are smaller

Most likely these are the remnants of the shoreline from when sea levels were much lower

Type of structure to prevent coastal erosion: Pt. 1

**Jetty** – built next to a tidal inlet to stabilize the location of the inlet 

Type of structure to prevent coastal erosion: Pt. 2

**Seawall** – exactly what it sounds like

Uninteded consequences of aforementioned erosion- prevention structures

*  expensive to build


*  degrades recreational beach!

An effective way to deal with costal erosion…

groins interrupt the wave reflection and capture sand as it is carried along the shore

What are the four processes that move river sediment?

Traction, Suspension, Solution, Saltation

What are the types sediment dispersed in rivers?

* Bed load


*  Suspended load
*  Dissolved load

What does competence of a river refer to?

**Competence** is size, controlled mostly by the current speed

What does capacity of a river refer to?

Number that can be carried, controlled mostly by discharge

Type of river that flows year round…

**Perennial** (Colorado River, Rio Grande)

Type of river that flows at certain times of year….

**Intermittent/Ephemeral** (Western USA, Alpine streams/creeks)

What is a **water table?**

zone in the ground where pores and fractures are saturated with water

How does topography effect the flow of water?

Topography influences how water is precipitated on, evaporated from, stored in, and routed through the landscape

**How does a river form and evolve? (Pt.1)**

During a rainstorm, water coalesces and causes ***rills*** (tiny rivers) 

**How does a river form and evolve? (Pt. 2)**

Headward erosion causes these rills to grow into gullies

How does a river form and evolve? (Pt.3)

Gullies organize into drainage basins

How do humans effect rivers? (Pt. 1)

 Changing channel pathways

* Building dams
* Building levees
* Channelizing river

How do humans effect rivers? (Pt. 2)

2) Changing amount of water:

* Paving flood plains and watersheds
* Diverting water for irrigation
* Depleting groundwater

Where are other places water is stored (other than rivers, lakes, ocean, etc)

Snowpack, wetlands, and ***in the ground***

What is ***porosity***?

how much pore space is present

* How many pores?
* How big are they?

What is ***permeability***?

how well water can move through sediments/rock

* interconnectedness of pores

What must aquifers be?

Must be porous ***and*** permeable

What are the best rocks/materials for aquifers?

**Sandstones** and **limestones**; shale is HORRIBLE

What controls the rate of groundwater flow? **(Pt. 1)**

Elevation difference of water table between h1 & h2

* greater difference in elevation = faster flow

What controls the rate of groundwater flow? **(Pt. 2)**

Distance traveled 

* *hydrologic gradient = elevation difference / distance traveled*

What controls the rate of groundwater flow? (**Pt. 3)**

Permeability of aquifer

* higher permeability = faster flow

Does groundwater move slow or fast?

It moves slow; Typical rates: \~0.5 – 1 m/day; on human timescale groundwater is non-renuable source

Where is contamination in ground water?

Near the surface and recent

What is one consequence of groundwater depletion?

The land sinks

Why is saltwater intrusion harmful?

Since salt water is more dense, so it rises to the top and is the first water to be pumped. Salt water is obviously not a replacement for groundwater

What is desertification?

* land degradation in dry climates 


* Reduction in productivity

What causes desertification?

* Climate


* Drought


* Anthropogenic
* Overgrazing
* Poor agricultural practices

How are deserts created?

Weathering process. Temperature variation between day and night causes stress to the rocks and break it down to sand.

Forms of desert erosion…

Water erosion (**flash floods**)

Wind erosion (grains bounce and ricochet, **saltate**)

The moons overall composition is made out of…

BASALT!!!

What are ventifacts?

sandblasted rocks on surface, forming smooth facets

Crescent shape dune, perpendicular to wind direction

Barchan dunes

Central sand piles with branching arms

Star dunes **(variable wind direction, multiple wind directions)**

Many parallel elongated ridges, wind from one direction

Transverse dunes (**perpendicular to wind direction**)

Horns point opposite to barchan, common in coastal dune fields

Parabolic dunes (**strong winds blow dunes into parabolas**)

Many parallel elongated ridges, limited sand supply, sand blowing in **2** directions

Longitudinal dunes (**crests are parallel to wind**)

a triangle-shaped deposit of gravel, sand, and even smaller pieces of sediment, such as silt

Alluvial fan

Ventifacts cover the ground of desserts and become…

desert pavement