Discussion 4
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Volcanic and Tectonic Landforms
(The Building Processes)
I. Introduction and Review
We begin by building mountains and landscapes; we will ultimately study their destruction
This begins our study of geomorphology, which is the study of landform process.
These processes include earthquake and volcanic activity. They are referred to as.endogenic processes, which means they are driven by Earth’s internal radioactive energy.
Any processes driven by external energy (the sun and weather) are exogenic processes.
II. Crustal Deformation Processes and Landforms: As a result of Plate Tectonics, the
lithosphere is under constant stress (compression, extension, shearing stresses).
A. Folding (compressional forces): (see text)
1. Syncline (see text)
2. Anticline (see text)
Folding (See text for simple diagram)
B. Faulting: •Faults are planar fractures (fault plane) in the Earth's crust along which slippage
(earthquake) occurs. They take many forms. •Found commonly at plate boundaries; but also elsewhere.
1. Normal Fault (extensional forces): Results in vertical movement of land.
Normal Fault
Normal Faults in a Series (Graben and Horst)
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2. Reverse Fault (compressional forces): Results in vertical movement of
land. Causes oversteepening, and subsequently, landslides.
Reverse Fault
3. Strike-Slip Faults (shearing forces): Results in side to side horizontal
movement. Leaves a fault trace, possibly a slight scarp.
Left Lateral Strike-Slip Fault (mapview) (with offset stream as an example)
Right Lateral Strike-Slip Fault (mapview) (with offset road as an example)
III. Earthquakes: Sudden slippage along a fault, occur at all types of plate boundaries, sometimes
far from boundaries.
A. Elastic Rebound Theory:
Helps to explain movement along faults.
Energy is stored as stress builds up; crust “bends” slightly.
Tectonic force exceeds friction force, resulting in sudden break along the fault.
B. General Terminology
1. Focus: The subsurface point where the actual break occurs.
2. Epicenter: The point on the surface directly above the focus.
3. Seismic Waves: Ripples of energy which pass through the crust.
C. Measuring Intensity and Magnitude
1. Seismograph: Measures vibrations caused by an earthquake.
2. Moment Magnitude Scale: Quantitative scale of the energy released. Each
whole number increase is a 31.5 fold increase in energy released. Represents the updated version of the old Richter Scale.
Over-steepened Fault
Scarp
(landslides frequent)
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D. San Andreas Fault
1. Type of Plate Boundary: Transform boundary between Pacific and North
American Plates. System includes many other related faults.
2. Type of Fault: Right Lateral Strike Slip Fault
IV. Volcanic Processes and Landforms
A. Volcanic Activity Primarily Associated with…
1. Convergent Plate Boundaries: Where subduction occurs
2. Divergent Boundaries: Sea Floor spreading centers or continental ruptures.
3. Hot Spots: Caused by a single stationary mantle plume. See further.
B. VOLCANIC ERUPTIONS AND VOLCANO TYPES OVERSIMPLIFIED
CHARACTERISTICS EXPLOSIVE ERUPTIONS EFFUSIVE ERUPTIONS
Type of Volcano Composite volcano
(steep sloped)
Shield volcano (gently sloped)
Sideview of volcano
(simple sketch)
Viscosity of Lava
(thickness of lava) High Low
Effects of viscosity (see text) (see text)
Mineral Composition
of Lava Mafic or Felsic? (see text) Mafic or Felsic? (see text)
Type of Rock(s) (see above) (see above)
Found in
Association with… Subduction
Sea-Floor Spreading and Hot Spots
Examples
Andes, Japan, Aleutians, & Cascade Range (Mt. St Helen's,
Mt. Hood, Mt. Shasta, etc.)
Iceland (Sea-floor spreading) & Hawaii (Hot Spot)
Layers of pyro- clastics (ash and
rock fragments)
Layers of cooled
rhyolite and andesite lava
Magma
Layers of cooled basalt lava
Magma
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C. Focus on Hot Spots
A hot spot represents a single point of volcanic activity, also referred to as a "stationary mantle plume"
As a plate moves across a hot spot, a chain of islands is formed (the Hawaiian Islands is a great example), with the youngest island is over the currently active hot spot, while the older islands have since moved away.
Studying this activity has helped scientists determine the 1) velocity and 2) direction of plate movement, including any major changes in velocity and direction in the past.
See below for how to calculate plate velocity
Plate direction is determined by drawing an arrow parallel to the islands, pointing toward older islands…
PLATE VELOCITY PROBLEM (see map below): How fast (in centimeters per year) is the Pacific
Plate moving over the Hawaiian Hot Spot? To figure this out, pick out two islands (with ages listed) along the Hawaiian Ridge. Follow this formula to calculate the rate:
[distance between islands (km) ] x [100,000 cm/km ] [age difference of island (yrs) ] = ??? cm/yr
D. Other Volcanic Phenomena
1. Pyroclastic Flow: This is a cloud of searing hot acidic gas and ash which travels like
a shock wave down slope, burning everything in its path.
2. Lahar: This is a mud/debris flow of volcanic origin. It occurs when the loose ash and
pyroclastic debris on the slopes of composite volcanoes become saturated. Can result from the rapid melting of ice and snow during an eruption.
3. Geothermal Activity (Hot Springs and Geysers): Ground water seeps into
cracks in the earth and comes into contact with hot rock. It then rises under pressure.
4. Circum-Pacific Volcanic Belt or “Pacific Ring of Fire” (See text)
Figure 8-19, pg
271 in
Christopherson
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V. Tsunami (may be called a seismic sea wave, but NOT a tidal wave)
A. Basic Description: A tsunami is a wave or series of waves traveling at very high
speeds (over 500 mph / 750 kph) with extremely long wavelengths (300 miles / 500 kilometers). It is not one large wave, bur rather it is the arrival of the ocean! A wall of over 30 feet of water may travel several miles inland, especially in low lying coastal areas.
B. Causes
1. Undersea Earthquakes (especially subduction!!!!!)
2. Volcanic Eruptions (coastal or undersea)
3. Coastal Landslides
4. Undersea Landslides
5. Meteor/Comet Impact
C. Recent Major Events
1. Tohoku Japan Quake and Tsunami (9.0 Mag, Mar. 11, 2011)
2. Indian Ocean Quake and Tsunami (9.2 Mag, Dec. 26, 2004)
Continue to next page for sample questions >>>>>>
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Sample Questions: Questions similar to these will be on your exam. As you study you should
anticipate how I might use these questions to create new questions on the same concepts.
1 Which is an example of an exogenic process? A. a volcanic eruption B. a river carving through a mountain
2
If this is an example of a left-lateral strike slip fault (seen from above), which two locations will become adjacent (next to each other) in the
shortest amount of time? V W X
Y Z
3 What type of faulting is shown in the diagram below? (diagram not shown here)
4
Assume that an earthquake with a magnitude of 4.6 and a depth of 14 km occurs in Smithville. Where is the focus of the earthquake?
A. 4.6 miles north of Smithville B. 14 km beneath Smithville C. 14 km south of Smithville D. 4.6 miles away from Smithville
5
The San Andreas Fault of California is an example of what type of fault? A. Normal Fault B. Reverse Fault C. Right Lateral Strike Slip Fault D. Left Lateral Strike Slip Fault
6
If this is a portion of the San Andreas Fault (seen from above), which two locations will become adjacent (next to each other) in the
shortest amount of time? V W X
Y Z
7
Which type of plate boundary will generally have no volcanic activity associated with it?
A. divergent B. convergent (oceanic / oceanic) C. convergent (oceanic / continental) D. transform
8 Where is there likely a chain of explosive volcanoes? (You will be shown a map on the exam.)
9 What characteristic (or characteristics) would you expect to find in a shield volcano?
10
You are on the island of Arewedoneyet. It is a volcano currently forming at an active “Hot Spot.” Approximately 1750km away there is
another island, which was formed 18.1 million years ago by the same hot spot. Based on these facts, how fast is the plate moving over
this hot spot?
11
You are on the island of Imsotired. It is a volcano which was formed at a “Hot Spot” 5.7 million years ago. Approximately 650km away
there is another island, which was formed 14.7 million years ago by the same hot spot. Based on these facts, how fast is the plate moving
over this hot spot?
12 Under what circumstances will a lahar most likely occur?
13
POSSIBLE ESSAY QUESTION: How does studying the position and age of the Hawaiian Islands help us understand plate tectonics?
Provide details.
14 POSSIBLE ESSAY QUESTION: Thoroughly compare and contrast the characteristics and results of explosive and effusive volcanic
eruptions (as covered in class!!!).
GOOD NEWS!!! The practice questions above - plus many, many more – can be found in the online practice quizzes
discussed in your syllabus and in class. You can take each quiz multiple times, and each time you will get some new questions. Once submitted, the quizzes are graded automatically, with the correct answers provided immediately. This is a great way to prepare for the exams!!!
SERIOUSLY, TAKE THE ONLINE PRACTICE QUIZZES!!!