Natural Science II – ERTH 1040 The Earth’s Surface J. D. Price
Keep in mind the major (and fundamental) sources of energy available to the surface of the Earth. •Heat transfer from the interior – which discussed in the previous lectures •Heat transfer from the Sun Radiation transfer from the surface of this star. Earth’s Surface There is only one other periodic source of energy external to the Earth: meteorite impacts
Heat redistribution from the Earth’s interior means: Volcanic eruptions Crustal uplift These build mountains (and lowlands) This leads to potentials in gravity (potential Earth’s Surface energy that may change into kinetic energy). Simply: stuff will move downhill
As we’ll see, the distribution of solar across the Earth’s surface (recall direct sunlight falls only between the tropics) drives the evaporation and precipitation of water. 1. Water vapor from low places is elevated to high places 2. Liquid water moves downhill* 3. Carries with it other Earth’s Surface materials *Most movement is underground
Earth’s Surface
Changes in deposition produces layers of sediments. Sequential layering – newer sediments deposited on older. Earth’s Surface Erosion exposes the layers and permits easy direct observations
Original horizontality Q: where are the oldest rocks in a sequence of layered sediments?
•Flat lying sediments are found forming in large packages today - gulf coast basin. •Smaller packages can be found in lakes, on river floodplains, adjacent to mountains. •The result of gravitationally driven erosion, transport, and deposition. Earth’s Surface •But what causes the gravity to be a force of deposition?
Deviatoric Stress Compression Extension Earth’s Surface Shear
Strain Earth’s Surface Q: What’s the difference between stress and strain?
Brittle - faulting Extensional (Normal) Compressional (Reverse) Earth’s Surface Parallel to stress (Strike slip or transform)
An example from Big Bend N.P. Boquillas Cañon, view to Mexico from Texas across Rio Grande Compressional or extensional? Earth’s Surface
Earth’s Surface Horst Graben
Fault block mountains Figure 20.17 20-405
Inclined Strata An example from Twin Mountains, near Canyon City, CO
Rotated half grabens Earth’s Surface
Earth’s Surface Series of N-S fault blocks make up the mountains of the Basin & Range.
Siccar Point, Scotland Devonian Earth’s Surface Silurian
Angular unconformity Inclined strata below (Arbuckle Group, Cambro-Ordovician) is eroded and covered by stream channel strata (Collings Ranch Conglomerate, Pennsylvanian). Represents ocean deposition, compression, extension, and stream deposition. Arbuckle Mountains, OK.
Ductile – folding All compressional Anticline Syncline Q: Why no extensional folding? What does extension do to ductile materials?
Thrust fault – low angle reverse Earth’s Surface Anticline and fault – brittle deformation is localized to the fault, ductile elsewhere.
Arbuckle Mountains, OK Earth’s Surface
Arbuckle Mountains, OK Rattlesnake Mountain, WY Glastonbury Anticline, CT Earth’s Surface
Ouachita Mountains, Oklahoma Earth’s Surface
Dome The Adirondacks are a prime example of doming. Note now orange (Ordovician) and light blue (Cambrian) colors wrap around the pink, dark blue, and stippled areas (1.2Ga rocks). Earth’s Surface Figure 20.16 20-404
Asymmetric folding Earth’s Surface
Asymmetric folding Earth’s Surface
Earth’s Surface
Earth’s Surface
Earthquake The ground motion associated with energy release during brittle deformation. Breaking transfers energy through surrounding material by moving it (seismic waves) Earth’s Surface
elastic rebound theory Earth’s Surface Figure 20.12 20-401
Fault-related earthquake Earth’s Surface Q: What is the difference between the epicenter and the focus?
locating earthquakes Q: How do the two different types of waves differ from each other? Figure 20.14 20-403
Earth’s Surface Q: What is the difference in ground motion between a magnitude 5 quake and a magnitude 6 quake?
Richter TNT for Seismic Example Magnitude Energy Yield (approximate) -1.5 6 ounces Breaking a rock on a lab table 1.0 30 pounds Large Blast at a Construction Site 1.5 320 pounds 2.0 1 ton Large Quarry or Mine Blast 2.5 4.6 tons 3.0 29 tons 3.5 73 tons 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) 5.0 32,000 tons 5.5 80,000 tons Little Skull Mtn., NV Quake, 1992 6.0 1 million tons Double Spring Flat, NV Quake, 1994 6.5 5 million tons Northridge, CA Quake, 1994 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon Earth’s Surface 7.5 160 million tons Landers, CA Quake, 1992 8.0 1 billion tons San Francisco, CA Quake, 1906 8.5 5 billion tons Anchorage, AK Quake, 1964 9.0 32 billion tons Chilean Quake, 1960 10.0 1 trillion tons (San-Andreas type fault circling Earth) 12.0 160 trillion tons (Fault Earth in half through center, OR Earth's daily receipt of solar energy)
Trinitrotoluene (TNT) Amounts of TNT are used as units of energy, based on a specific combustion energy of TNT of 4.184 MJ/kg = 1 calorie per milligram = 1.9 MJ per pound But…it’s not just the energy but the rate at which it’s delivered (power). The Earth receives 6.08 E 17 MJ of energy from the sun but over Earth’s Surface a day (6.08 E 17 MJ / 8.6 E 4 s) 7.037 E 12 MW And…it’s also the area on which its applied Earth = 4 � r e 2 = 5.10 E 8 km 2 ) The Earth receives 1.38 E 4 MW/km 2 of sunlight
Earth’s Surface
NBC miniseries “10.5” 20 million viewers tuned in to watch a story based on a west- coast destroying earthquake Earthquake magnitudes are a function of the length and depth of the fault A 10.5 could only occur on a fault that encircles the globe more than once. Earth’s Surface Good new for bad science - a sequel has been filmed.
In absence of a seismometer, the intensity of an earthquake may be approximated using the modified Mercalli Scale Likewise, you can compare the type of damage done Earth’s Surface knowing the Richter Scale.
The 1964 Good Friday Earthquake - Valdez, Alaska - largest historical quake in the U.S. house Earth’s Surface
Earth’s Surface
The earthquake produced a landslide and a tsunami Locomotive engine Earth’s Surface Local land surfaces were noticeably uplifted
The tsunami was the second to hit the pacific in 4 years Earth’s Surface
Volcanoes Where partial melts of the Earth’s Interior reach the surface. •Partial melts – magmas (mostly liquid with some solid) •These are hotter than surroundings – lose heat and solidify •These originate at depth – depressurize as they ascend Earth’s Surface Q: What determines the nature of a volcanic eruption? How do these factors influence the morphology of a volcanic structure?
The shape given to volcanic edifices is due to its eruptive style. It’s eruptive style is due to magma: Composition – including dissolved gasses Low Si – more fluid High volatiles – more explosive Supply rate – material from the Earth’s interior Fast – frequent eruptions from same vent Earth’s Surface Slow – vents solidify, more explosive The nature of an eruption is a function of the pressure of the magma.
Kilauea, Hawaii March, 1996 Q: What are some common volatile components in a magma?
shield volcano Earth’s Surface Generally low Si Hawaii: Hot asthenospheric mantle, below provides hot material that intrudes Low volatile lithosphere and melts below oceanic crust. High rate
Mauna Kea, Hawaii Cinder Cones Shield Q: What tectonic feature produces volcanism in Hawaii?
Pu’u Hulu Mauna Loa, Hawaii Pahoehoe Q: What are the names given to these two types of lava?
Kalapana Gardens Kilauea, Hawaii
Earth’s Surface Fissure
Cinder Cone Low Si High volatile high rate Earth’s Surface
Mauna Kea, HI Mauna Loa Summit Cone, Mauna Kea
Pu’u O’o cone Q: What does this lava lake signify in terms of volatiles?
Composite volcano Mixed but generally Composite volcanoes build up Higher Si over time from localized vents. High volatile Low rate
Earth’s Surface
Mount Saint Helens is an example of a composite stratocone - the locus of Mount Saint Helens: pre 1980 volcanism for hundreds of thousands of years Q: What tectonic feature produces volcanism in the Cascades?
In 1980, the mountain began to erupt small plumes of ash from an area near the summit. The first eruption in the conterminous US since that of Mount Lassen (northern California) in 1914. Earth’s Surface Mount Saint Helens: March, 1980
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