Download measuring the earth - Mepham Earth Science

MIDTERM TEST NOTES REVIEW
UNIT 1
1) AN OBSERVATION always involves the use of the senses. Instruments may extend the
senses.
2) AN INFERENCE is an interpretation or conclusion based on observations. Inferences
usually involve what happened in the past. Any statement about the future MUST be an
inference.
3) CLASSIFICATION is the grouping of items based on common characteristics. We classify
things to make them easier to study and to understand.
4) MEASUREMENT:
A) Mass: The amount of matter in an object. The basic unit of mass is the gram.
B) Volume: The amount of space occupied by an object. The basis units of volume are
the cm³ and ml. They are equal.
5) DENSITY: Amount of mass per unit of volume. You MUST be able to solve for any value
(m, d, or v) in the density formula.
a) Density is expressed in g/cm³ or g/ml
b) Cut an object into many pieces and the density of each piece remains the same.
c) Compress an object (reduce its volume) and the density increases.
d) When an object expands (increases in volume) its density decreases.
HOT = EXPANDS = LESS DENSE = RISE
e) The density of water is 1 g/cm³ (1 g/ml) at 3.98oC
f) Water reaches maximum density at 4oC (really 3.98oC)
6) PHASES of MATTER: a) Solid (usually most dense)
b) Liquid
c) Gas or vapor (least dense)
7) CHANGES are EVENTS; All can be described in terms of "time and space (distance)".
All changes require time and all require something to move a distance through space.
a) Rate of change varies greatly. Some are fast (earthquakes). Some are slow (evolution).
b) Changes may be cyclic; repeating again and again. Cyclic changes like the phases of
the moon are predicable.
1) Predictions are most accurate when data is gathered over a long period of time.
c) Changes may be non-cyclic; these are one time events such as meteorite impacts
which are usually not predictable.
d) All changes involve a flow of energy. Energy is exchanged at an interface. An
interface is a boundary between two different materials (land and water, air and
land).
c) The “law of conservation of energy” states that “Energy cannot be created nor
destroyed but one kind of energy can be changed into another.”
Example: Sunlight falls on your face. It is changed from light to heat. You feel the
warmth of the sun.
Example: A rock rolls down a hill. Potential energy stored in the rock is
converted to kinetic energy as the rock gathers speed.
9) GRAPHS;
> Express relationships between 2 variables, dependent and independent.
> Y axis = dependent variable, X axis is the independent variable. Time is always independent.
The relationship may be DIRECT (two variables increase or decrease together)
a) Direct relationships: All of these graphs below show a direct relationship. Both values
increase or both decrease. The line moves up and away from the origin.
b) Inverse relationships: All the graphs below show an inverse relationship. As one value
increases the other decreases.
Rate (of change): The amount of change per unit of time. RATE = SLOPE = GRADIENT. If the
graph line is straight, the rate is constant (see graphs below)
If the line is curved the rate is changing. If the curve gets steeper the rate is increasing. If the curve
is getting less steep the rate is decreasing. (see graphs below)
Getting steeper.
Rateincreasing.
Getting less steep.
Rate decreasing.
MEASURING THE EARTH
A) ????????????The shape of the Earth:
a) An oblate spheroid (flattened sphere)
b) Flattened at poles
1) polar circumference 40,008 km
2) polar diameter 12,714 km
c) Bulging at the equator
1) equatorial circumference 40,076 km
2) equatorial diameter 12,757 km
d) From space the Earth appears to be a perfect sphere
B) ??????????Evidence for Earth's shape (ROUND vs FLAT)
a) Photographs of the Earth from space or the moon (this is the best evidence because it’s
a direct observation).
b) Earth's shadow seen on moon during eclipse.
c) Ships disappear over horizon bottom first.
d) Altitude of polaris varies with latitude.
e) Angle of noon sun varies with latutude.
C) ?????????????Evidence for Earth's shape (OBLATE SPHEROID)
a) Gravitational measurements:
1) stronger at poles (closer to center)
2) weaker at equator (further from center)
b) Altitude of polaris does not match latitude. Moving 1o north or south
on the earth’s surface does not always result in a change of exactly 1o
in the altitude of Polaris. If the earth was perfectly round this slight
difference would not occur.
D) ?????????Determination of circumference
a) Eratothenes experiment
1) Get angle of noon sun at 2 locations on the same meridian (N-S line)
2) Find difference between 2 angles
3) Get distance between 2 locations
4) Divide difference into 360E
5) Multiply result by the distance = Circumf.
360
Circumference = ------------------------- X Distance
(Angle 2) - (Angle 1)
E) ??????Diameter of the Earth
a) D = 2r
b) D = (2) (6.37 X 103)
c) D = 12.74 X 10³ or 1.274 X 104
F) Hydrosphere
a) Water (salt and fresh) covering 70% of the Earth
b) Averages 3.5 - 4.0 km in depth
c) Oceans represent <1% of thickness of Earth
G) Atmosphere
a) Gas envelope surrounding Earth
b) 78% nitrogen, 21% oxygen, 1% other
c) Extends to approx. 150 km.
d) Layers:
1) Troposphere (0 to 12 km)
2) Stratosphere (12 to 50 km)
3) Mesosphere (50 to 82km)
4) Thermosphere (82+ km)
e) Interfaces between layers are "pauses"
1) Tropopause
2) Stratopause
3) Mesopause
H) Lithosphere
a) Solid, rocky, outer shell of the Earth. (Covered by regolith, the loose rock & soil)
b) Averages 20-25 km.
c) Thicker under continents - thinner under oceans.
POSITIONS ON THE EARTH
A) Coordinate system (grid)
a) Latitude (aka parallels)
1) Measured in degrees/minutes
2) 60 minutes = 1 degree
3) Run east-west
4) Change north-south
5) Maximum latitude = 90E (N or S poles)
6) Minimum latitude = 0E (equator)
7) Size of a degree varies with latitude due to shape of the Earth
8) Altitude of Polaris = latitude (N only)
b) Determination of latitude
1) Draw line to horizon
2) Draw line to Polaris
3) Angle formed by these lines is equal to the latitude
4) Applies to Northern hemisphere only
c) Longitude (aka meridians)
1) Measured in degrees/minutes
2) Run North-south connecting poles
3) Change north-south
4) Prime meridian (0E) through Greenwich Eng.
5) Time changes 1 hour per 15E long. change
6) West = earlier / East = later
B) Fields
a) Region of space w/measurable values
1) Examples: elevation/temperature/pressure
b) Scalar fields
1) Values have magnitude only
2) Examples: elevation/temperature/pressure
c) Vector fields
1) Values have magnitude and direction
2) Examples: Wind/magnetic fields
C) Gradient (aka slope, rate of change)
change in field value between 2 points gradient
= ---------------------------------------------change in distance between 2 points
D) Isolines
a) Lines on a map connecting points of equal value
b) Special isolines:
1) Isotherms - equal temperature
2) Isobars - equal atmospheric pressure
3) Contour lines - equal elevation
c) Interval - value difference between adjacent lines
d) Index isoline - marked with its value
e) Isolines interval small (close) = steep gradient
Isoline interval large (far apart) = gentle slope
f) Contour lines seem to point in opposite direction of stream flowing
across them (point uphill)
g) Sea level = 0 elevation
h) Contour lines w/hatch marks = slope downward
i) Max elevation is a value higher than the highest contour line but less
than the next WOULD be.
E) Map legend
a) Gives distance scale (km and/or miles)
b) Key to symbols of man-made and natural features
c) Indicates direction
ROCKS & MINERALS REVIEW
A) Mineral: Naturally occurring solid substance with a definite chemical
composition.
1) not necessarily inorganic - coal and limestone are organic
2) not necessarily crystalline - sulfur, coal, and many more are
amorphous minerals (amorphous - having no definite shape or
pattern)
3) Minerals are identified by various properties:
a) color
b) hardness (1 - 10 on Moh’s scale) 1= talc (soft), 10 = diamond
(hard)
c) streak (color of mineral in powdered form)
1) pyrite is gold but its streak is black
d) luster (reflective qualities of surface) - metallic, dull
e)
cleavage: the tendency to break along
predetermined lines (cleavage planes)
1) This applies to crystalline minerals only
2) Non-crystalline minerals such as glass do not
cleave, they fracture.
f) taste (halite - salt) or smell (sulfur)
4) Physical properties are determined by the internal arrangement
of atoms:
a) Crystalline: minerals which have a regular, repeating
pattern of atoms or molecules. Such minerals break along
predetermined lines called cleavage planes. Examples:
1) salt - halite (cubic crystals)
2) quartz: silicon-oxygen tetrahedron
b) Amorphous: no crystal structure: coal, glass
1) NO CLEAVAGE - FRACTURE
c)
Diamond, graphite, and coal are all minerals made from the
same atom, carbon but they have very different physical
properties because they have different internal arrangement
of atoms.
5) Most minerals are made of the same few atoms because they are
the most abundant: see reference tables (most abundant elements
in crust & lithosphere). Different combinations of these same
atoms produce many different kinds of minerals.
6) The silicate minerals are the most abundant. They are formed
from silicon and oxygen (SiO2) with the atoms arranged into a
4-sided structure called a tetrahedron. Quartz is a common
silicate mineral.
The silicon atom is at the center and it is
surrounded by four oxygen atoms.
ROCK REVIEW
SEDIMENTARY ROCKS:
A. CLASTIC: fragmental particles cemented together.
1) They are classified according to particle size.
2) Only rock containing FOSSILS.
B. NONCLASTIC (evaporites):
1. Crystals from chemical precipitates (dolostone, rock gypsum).
2. Fossil limestone & Bituminous coal.
KEY TERMS: > Burial - compaction - cementation (of sediments)
> Precipitation from evaporating seawater.
> Form a thin VENEER over the surface of the Earth.
> Sediments deposited in LAYERS.
> May contain FOSSILS, RIPPLE MARKS, and MUD CRACKS
IGNEOUS ROCKS:
A. INTRUSIVE (Plutonic)
Slow cooling within the Earth = large crystal grains*
*large crystal grains = coarse texture
B. EXTRUSIVE
(Volcanic)
1. Ultra-fast cooling = no crystals = glassy
2. Fast cooling on surface = small crystal grains*
*small crystal grains = fine texture
KEY TERMS: > Melting - solidification of molten material (magma or
lava)
> Intergrown crystals
> Magma - lava
Note the diagrams below taken from Regents exams. Diagrams 1 and 2
represent IGNEOUS rocks. The mineral grains (crystals) are intergrown
with no spaces between them. Diagram 3 is a sedimentary rock such as
sandstone or siltstone. The grains here are not intergrown. There are
spaces between them. The grains are cemented together where they
contact one another.
(1)
(2)
(3)
METAMORPHIC ROCKS:
These are rocks that have been CHANGED by heat and/or
pressure but have not melted. Pressure increases density and
reduces porosity.
1) REGIONAL - a large area, perhaps thousands of square
miles, has undergone metamorphism. Example: The
Adirondack mountains of New York State. (heat and
pressure)
2) CONTACT - a small area of rock has been altered by direct
contact with magma or lava. Example: Rock surrounding an
igneous intrusion.
(heat only)
KEY TERMS: > Heat and/or pressure
> Alignment of minerals or crystals
> Recrystallization
> Very large crystals
> Banding of minerals
> Distortion of structure ---------------->
> Foliation
WEATHERING, EROSION, and DEPOSITION REVIEW
Weathering: The breaking upofrock from largeparticles tosmaller particles.
a) This Increases surface area of the rock which speeds the rate of chemical
weathering.
b) Rock weather on the surface of the earth only. Rocks underground or under- waterdo
not weather.
There are 2 basic kinds of weathering:
a) Chemical weathering
1) Changes the material (ex. iron into iron oxide - rust)
2) Surface phenomenon - reactions occur on the surface of rocks, not inside
them (usually).
3) Like most chemical reactions, water is required.
4) Hotter = faster
5) Fastest chemical weathering occurs in warm/moist climates
a) oxidation (ex. iron combines with oxygen to form rust)
b) hydration - minerals in rocks combine with water.
c) carbonation - rocks, especially limestone react with
carbonic acid.
6) Depends on KIND of rock. Some rocks (limestone) are chemically
reactive. Other rocks (quartz) tend not to react with chemicals.
b) Physical weathering (also known as Mechanical weathering).
1) Frost action: Water gets into cracks - freezes - expands - enlarges the
crack. Requires alternating freeze-thaw cycles.
2) Wave action: Waves pounding against rocks -sand and rocks inthe
waves help to break up the shoreline.
3) Stream abrasion - The rounding and smoothing of rocks as they tumble
in a stream. These rocks are the ‘cutting tools’ of the stream which
‘downcut’ the stream’s V-shaped channel as they roll along.
4) Wind abrasion - Important in dry climates. The wind picks up sand and
blows its against rocks causing ‘pitting’ (sandblasted appearance).
5) Root Wedging - Plant roots grow into cracks in rock and split them.
6) The rate of physical weathering depends on the resistance (hardness)
of the rock and on the kind of climate.
Weathering is necessary for the formation of soils. If rocks didn’t weather there would be no minerals
in soils which are needed by plants and animals.
Erosion (Leveling) - transport of sediments from one place to another.
A) Gravity is FORCE driving all erosion
1) Rocks found at the base of a cliff got there by gravity only.
B) Agents of erosion:
1) Running water is the dominant (most important) agent of erosion in
most places on Earth today.
a) How does running water transport particles?
1) in suspension
2) by floatation
3) rolling along the bottom (saltation/traction)
4) in solution
> Key concepts of water erosion.:
1) V-shaped stream channels are a sign of water erosion.
2) The rate of stream erosion depends on the velocity (speed) of the stream.
Velocity of the stream depends on:
> slope (steep = fast)
> stream volume (aka discharge - More volume = faster)
> shape/size of channel (if channel narrows velocity increases)
3) Fastest stream flow occurs on the outside of a curve (erosion)
Slowest on inside of curves or where entering lake or ocean (deposition)
Fastest stream flow occurs also occurs at a point farthest from the bottom
and the sides where drag
occurs.
Straight - fastest in center.
Deepest in center
Fastest on outside of curve
Deepest on outside (C)
Fastest on outside of curve
Deepest on outside (F)
> Flow is fast if the channel is narrow. The rate slows if the channel widens or if the stream enters
a lake or the ocean.
> Sediment carried in suspension is always moving more slowly than the water of the
stream.
Outside of curve = faster = erosion.
Inside of curve = slower= deposition
The arrows show stream velocity. Big arrow = fast. Small arrow = slow. Water drags
along the sides and bottom so it goes fastest at the center near the surface.
How does stream abrasion affect the rocks being carried?
>Particles transported by a stream become:
ROUNDER - SMOOTHER - SMALLER
Stream deposition:
When a stream slows it deposits sediment it can no longer carry.
Streams SORT the sediment they deposit according to:
> SIZE: Biggest settle fastest. They are on bottom, smallest on top
> DENSITY: Most dense settle fastest. Most dense on bottom. Least dense on top
> SHAPE: Round settle fastest. Round on bottom. Flat on top.
> Vertical & horizontal sorting of materials are the hallmarks of stream deposition.
Vertical sorting
Horizontal sorting
Colloids are the smallest particles and take longest (months) to settle.
> Materials in solution (salt) NEVER settle out but can precipitate down if
the water evaporates.
Young streams - Steeper - Faster
Old streams - Nearly flat slope - Slower
Very old streams form ‘meanders’ (see below) and “Oxbow Lakes”
Wind erosion - not really significant except in dry climates.
1) Pitted rocks (sandblasting)
2) Only small particles can be carried by wind.
3) Sharp, angular, landscape features - Mesas and arches such
as those found in the American southwest.
The amount of erosion in a region will also depend on the characteristics of the bedrock in the
area. In the diagram above, layer A protrudes because it has been eroded least.
This is because it is hard, resistant rock. Layer B, a soft rock, has experienced the greatest amount of
erosion. Layer C is the hardest, most resistant rock and has been eroded least.
NOTE: Even though the same forces have been at work on this entire region, the surface is unevenly
eroded because of the different types of rock that are exposed.
ENERGY IN EROSION - DEPOSITION SYSTEMS:
A) Energy in an erosional - depositional system.
Remember - Ke is the energy of motion
Pe is the energy of position (higher up = more Pe)
Earth materials that are at high elevations have high Pe (because they are high up)
but no Ke (since they are not moving).
Erosion increases the Ke by moving material but decreases the Pe because the material is always
moving downhill due to gravity.
Finally, when material is deposited at a lower elevation, it has no Ke and has lost Pe.
So, when all is said and done, erosion and deposition lower the total energy.
Additional material:
Q: If erosion is a constant process, why hasn’t the earth been worn flat?
A: Because erosion is opposed by the forces of uplift. In any area one force is
usually dominant over the other. If the forces of erosion (leveling) and uplift
were equal, then the elevation would remain constant and a condition of
equilibrium would exist.
In NYS, erosion is dominant over uplift. Landscape elevations are decreasing.
If erosion (leveling) is dominant, then elevation
decreases. If uplift is dominant, then elevation
increases.
If the 2 forces were in dynamic equilibrium, then the elevation would
remain unchanged.
SOILS:
A: Residual soils: Formed from the bedrock immediately beneath them and have
chemical properties similar to the bedrock.
1) These are rare because erosion usually transports weathered particles far from their
original location.
B) Transported soils: Rock particles formed in one location and
transported to another
1) These are most common.
2) All the soil in NYS is transported from somewhere else. Most soil was
removed during the last ice age.
C) Soil consists of weathered rock particles and organic material from plants
and animals. The faster rocks weather and the more plants grow, the thicker the soil
becomes.
Vocabulary: The are terms you must know. If you don’t, go back into the review above and find
them:
Chemical weathering
Wind abrasion
Stream discharge
Resistant rock
Physical weathering
Floatation
Sediment
Residual soil
Mechanical weathering
Saltation
Sorting
Transported soil
Oxidation
Solution
Unsorted
Pe and Ke
Carbonation
Agent
Valley (alpine) glacier
Energy of position
Hydration
Suspension
Parallel grooves
Leveling force
Frost action
V-shaped valley
Scratched & polished
Uplift
Ice Wedging
U-shaped valley
Erratic
Dynamic equilibrium
Wave action
Erosion
Drumlin
Continental glacier
Root wedging
Deposition
Kettle lake
Meandering stream
Stream abrasion
Settling (rate)
Pitted surface
Colloids
The Dynamic Crust
1) Virtually everything you need to know about the interior of the earth can be
found on page 10 of your reference tables. Take the time to become familiar
with page 10 and everything on it.
A) The crust:
1) Oceanic crust – basalt rock - thinner - higher density younger(because new sea floor crust is always being created while
old floor is subducted).
2) Continental crust – granite rock - thicker - lower density - very old
(because it
(just floats around “original crust of planet”).
B) The Mantle:
1) MOHO: The interface (dividing line) between the crust and the rigid
mantle beneath.
2) Asthenosphere (plastic mantle): Layer of relatively flexible (plastic) rock
that can (convection currents) flow because it is at or near its melting point.
3) Stiffer mantle: As the name implies the rock here is less plastic but it
can still flow very slowly (convection currents)
IMPORTANT: It is believed that the force driving continental drift is convection currents
in the upper mantle.
4) Outer core: Liquid. Mostly iron and some nickel. Convection currents
here are probably responsible for the earth’s magnetic field.
5) Inner core: Solid. High pressure keeps the iron/nickel core from melting.
2) EVIDENCE FOR CRUSTAL MOVEMENT
NOTE: Law of Original Horizontality - Sedimentary rock layers are always deposited horizontally as
continuous layers. Thus, if a layer is tilted, broken, folded, or otherwise deformed, it must
have moved after it was deposited.
Displacement of rock layers (strata)
a) Tilting: sedimentary rock layers are tilted (no longer horizontal)
b) Faulting: sedimentary rock layers are broken - probably by earthquake activity.
c) Folding: sedimentary rock layers are folded and squeezed by pressure in the crust.
(see diagrams below)
d) Shallow water marine fossils (clams, scallops, etc) at high elevations in mountains.
This is evidence that the crust has been uplifted.
e) Shallow water marine fossils in deep marine deposits (geosynclines).
A geosyncline is an unusually thick (thousands of feet) deposit of sedimentary rock that
often accumulates at the mouth (delta) of large rivers. If clams are
found 5,000 feet below the ocean bottom it is evidence that the crust has subsided (sunk).
2) CONTINENTAL DRIFT (THEORY OF PLATE TECTONICS):
Theory: The earth’s crust is divided into numerous pieces (plates) that are in motion
relative to one another. There are 2 types of plates:
a) Continental plates made of granite. These are low density and are floating= on
the underlying basaltic plates below. They are very, very old.
b) Oceanic crust made of basalt. These form the sea floor .New oceanic crust is
continually being produced at mid-ocean ridges(sea floor spreading). Old
oceanic crust is continually being destroyed as it is
subducted into the mantle and melted. Thus, oceanic crust is not very old.
c) The force driving the continents is convection currents in the mantle which
cause the continents, which are floating on the mantle to drift around.
EVIDENCE FOR CONTINENTAL DRIFT and SEA FLOOR SPREADING:
1) >Fit= of the continents: The continents seem to fit together like pieces of a jigsaw puzzle that was together as one piece in the distant past.
2) Correlation of rocks from opposite areas of continents (see diagram).
3) Correlation of fossils from opposite areas on continents.(see diagram)
If rocks and fossils from area A= are the same as rocks and fossils
found at area B= even though these regions are separated by 2500 miles
of ocean, this is powerful evidence that once, in the distant past these
two areas were connected and were part of a single landmass.
4) Age of the sea floor:
a) Youngest rock at mid-ocean ridge where new sea floor is created.
b) Oldest rock is found near continents where old sea floor is subducted
and recycled.
c) Rocks equidistant from the mid-ocean ridge in opposite directions
are of the same age.
The rocks at location A and E are the oldest. The rocks at B and D are of the
same age because they are equidistant from the ridge in opposite
directions.
5) Paleomagnetism: Corresponding bands of normal and reversed magnetic
polarity in the rocks on either side of the mid-ocean ridge.
6) Actual laser measurement of the changing distance between continents.
Measurements of the distance between North America and Europe made
by bouncing laser beams off reflectors left on the moon show that continental
drift continues to this day. The continents are moving at the rate of 2 - 3 cm/yr.
Plate Boundaries:
There are several kinds of plate boundaries (places where different plates meet)
a) Convergent boundaries: 2 plates come together.
b) Divergent boundaries: 2 plates move apart.
c) Transform boundary: 2 plates slide past one another.
See map on page 5 of your reference tables.
This diagram shows a convergent boundary where basaltic oceanic crust meets
granitic continental crust. Because the oceanic crust is more dense, it is subducted
forming a trench. It sinks down under the continent back into the mantle where it
melts. The melting magma rises causing volcanos and earthquakes in the region.
HOT SPOTS:
Hot spots are plumes of rising magma that come from deep within the mantle. These
plumes are extremely stable lasting for millions of years and generally staying in one
place.
While a plume may stay in one place, pieces of the crust drift over it. As a piece of
the crust, oceanic or continental, moves over the hot spot volcanoes erupt and
islands may form. As a volcano moves off the hot spot it becomes extinct (no
longer erupts) and a new volcano may form on the crustal plate that is now over the
rising plume of magma.
This creates island chains such as the Hawaiian and Galapagos islands.
Closer to home, Yellowstone National Park is a collapsed volcano (a caldera) which
is sitting over a hot spot. It is likely to erupt again someday.
Note that Kilauea is the
youngest volcano and is
still erupting because it is
still over the hot spot. As
you look toward the NW,
the islands become older
and older. These are
extinct volcanos which
used to be where Kilauea
is today but they have
drifted, with the Pacific
plate, off the plume.
EARTHQUAKES:
1) Earthquakes occur primarily at plate boundaries. They usually occur at
shallow depths in the crust in regions where plates come together.
a) FOCUS: Point in the earth where the rocks slip causing an earthquake.
b) EPICENTER: Point on the surface directly above the focus.
Notice that the locations of earthquakes coincides with the map of plate
boundaries on page 5 of your reference tables.
2) Earthquakes generate waves which move through the earth:
a) P (primary) waves - FAST - move through solids and liquids.
b) S (secondary waves - SLOW - do NOT move through liquids.
3) Earthquake waves are detected by instruments called seismographs
4) Seismographs make paper records of a quake called seismograms (see below)
Data from one seismograph can tell you how far you are from an epicenter but it
takes data from at least three seismographs to tell you exactly where an earthquake
occurred. (see below)
A,C,and D= represent the location of seismographs. Each circle shows the distance between
the seismograph and the epicenter of an earthquake. The epicenter could be anywhere
on a circle. But when three circles from three different seismographs are put together, the
point where the circles meet is the location of the epicenter. Here, the epicenter of the
earthquake is at location B.
6) Sometimes a seismograph may receive only P waves from an earthquake or perhaps
no waves at all.
a) If only P waves are received it is because the S waves were absorbed by the
liquid outer core of the earth (remember, S waves cannot pass through liquids).
b) If no waves are received, it is because the seismograph is in a shadow zone
for that particular quake:
A shadow zone is caused by the
bending of earthquake waves as they
move from one layer to another.
Sometimes they are bent around a
particular seismic station which would
then receive no waves from that
earthquake. See diagram’
How To Use The Earthquake Travel Time Chart
(Reference Tables - Page 11)
1) Note:
a) Distance (bottom axis) is in thousands of kilometers and that each thousand
is divided into 5 smaller boxes so that each smaller box is 200 km.
b) Travel time (vertical axis) is in minutes and each minute is divided into 3
smaller box so that each smaller box is 20 seconds.
2) Below are ALL the facts about a particular earthquake. Each problem will give you
SOME of the facts and ask you to find ONE of the other facts.
FACTS:
a) Time of quake: 1:20:40 PM (20 minutes and 40 seconds after 1 PM)
b) Distance from epicenter to seismic station: 5200 km
c) P wave travel time from epicenter to station: 8:40 (8 minutes and 40 seconds)
d) S wave travel time from epicenter to station: 15:20 (15 minutes and 20 seconds)
e) Difference in P - S wave arrival times: 6:40 (6 minutes and 40 seconds)
This is the time interval between when P waves arrived and when S waves
arrived. The time between D and E or B and C on the chart.
f) Time P waves arrived at the station: 1:29:20 PM (The P waves would arrive
8 min. and 40 sec. after they started out. They started at 1:20:40 so just add
8:40 to their start time. But remember that you are adding seconds so 80
seconds = 1 minute and 20 seconds.)
g) Time S waves arrived at the station: 1:36:00 PM (The S waves arrived 15 min.
and 20 seconds after they started which was 1:20:40. So add 1:20:40 and
15:20)
3) The problems:
q1) How long will it take P waves to travel 5200 km?
a1) Find 5200 km on the bottom line (A). Go up to the P wave line (B). Go left to the vertical
axis (D) and read the time: 8:40
q2) It takes P waves 8 minutes and 40 seconds to travel from the epicenter of an earthquake to a
seismic station. How long will it take S waves to travel to the same station?
a2) Find 8:40 on the vertical axis (D). Go to the P wave line (B). Go straight up to the S wave
line (C). Go left and read the time (E) 15:20
q3) If a seismic station is 5200 km from the epicenter of an earthquake, how long
after P waves arrive will the S waves arrive?
a3) Find 5200 km on the bottom axis (A). Go up to the P wave line (B). Count the
time interval between (B) and (C): 6:40
q4) A seismic station is 5200 km from the epicenter of an earthquake. The earthquake occurs
at 1:20:40 PM. At what time will P waves arrive at the seismic station?
a4) Find 5200 km on the bottom axis (A). Go up to the P wave line (B). Go left and read the time
on the vertical axis (D). The time you should read is 8:40. This is how long the P waves
must travel to reach the station. If they started out at 1:20:40 then you must add the travel
time to this value:
1:20:40
+ 8:40
Remember that when adding seconds, each
---------------60 seconds is a minute. 80 seconds is one
1:29:20
minute and 20 seconds.
q5) P waves arrive at a seismic station at 1:29:20 PM. S waves from the same earthquake
arrive at 1:36:00 PM. How far is the seismic station from the epicenter of the
earthquake?
a5) First we must find the difference in arrival times between P and S waves.
1:36:00
- 1:29:20
---------------6:40 = the difference.
Now find the place on the graph where the space between the P and S lines is 6 minutes
and 40 seconds*. This is exactly between B and C. Follow the line from C to B straight
down and read the distance: 5200 km
Helpful hint. To quickly find the place where the difference between the P and S lines is
6:40, do this: Take a blank sheet of paper and place one edge on the vertical axis (time).
Mark off two points on the paper: 0 and 6:40. Now slide the paper keeping the 0 mark
on the P line. Keep the edge of the paper straight. When the 6:40 mark is exactly on the
S line look straight down the edge of the paper. It should be on the 5200 km mark.
1) Erosion by ice (glaciers)
A) Varieties:
a) Valley or Alpine glacier (small, local - between mountains)
b) Continental (global ice sheets such as those covering Antarctica today)
B) Evidence of glacial action:
a) parallel grooves cut into rocks
b) U-shaped valleys
c) scratched & polished rock.
d) erratics - large boulders that are unrelated to the bedrock
beneath them.
e) deep parallel lakes (The Finger Lakes of NY)
f) unsorted sediments (large and small particles all mixed
together
kettle lakes - formed when buried blocks of glacial ice melt creating a depression which fills with
water. (see below)
g) drumlins - Long, narrow mounds of unsorted glacial
sediment aligned in the direction of glacial movement.
Drumlins as they appear on regents exams. The glacier that deposited these was moving from left to
right.
Stages in the formation of a kettle lake Unsorted
material (mixed large & small particles)
typical of glacial deposition.
Landscape Review
Landscapes form as the result of 2 opposing forces: Uplift (mountain building) and Leveling
(erosion). Almost always one force is dominant over the other.
a) If uplift is dominant, the elevation of the landscape will increase.
b) If leveling forces (erosion) are dominant, the elevation will decrease.
c) If the two forces are in equilibrium, the elevation will remain constant.
1) PLATEAU - - - - - - - - - High elevation - - - - flat slopes - - - - horizontal bedrock
2) PLAINS (Lowlands) - - Low elevation - - - - flat slopes - - - - horizontal bedrock
3) MOUNTAINS - - - - - - High elevation - - - - steep slopes - - - tilted or folded bedrock
Effects of Climate:
a) Arid (dry) climate = sharp angular features (mesas of the SW).
b) Humid climate = rounded features
Rock types:
formation
Differences in the resistance (hardness) of rock may result in the
of mountains, cliffs, and other features as soft rock is warn away leaving
harder rock behind.
In this diagram of folded
bedrock, layers D and O are
resistant (hard) while layers C,
S, and M are softer. The
differences in resistance
explains the long ridges of
mountains formed by layers D
and O.
The cliffs that have formed in this
landscape region are the result of
differences in the hardness of the rock.
Soft rock is eroded away while harder,
more resistant rock remains forming cliffs.
The views above show the landscape as it appears in the surface and in cross section. Below each
diagram is the drainage or stream pattern associated with that landscape. Given any landscape,
you must be able to select the stream pattern associated with it. If you are given a steam pattern,
you must be able to identify the landscape in which that pattern would be found.
Also remember:
Stream or river valleys: V-shaped
Glacial valleys: U-shaped