10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 1MAR110 Lecture #3 Earth Interior-the Basis for Plate Tectonics Figure 3.1 Tsunami “Triggers” Four processes that can trigger a tsunami. Clockwise from upper left: volcanic explosion, underwater faulting, meteor impact, landslide. In order for a tsunami to be generated a large volume of water must be displaced. (NG)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 2 Figure 3.2b Density TThhee density of a material is the amount of that material contained in a “unit volume” such as a cubic centimeter (or cubic meter). In short , mass per unit volume or mass DENSITY = ----------- volume The material’s density can change because the amount of material within a fixed (or unit) volume can depend on its temperature. This is because temperature T change cause the material to expand or contract.. Figure 3.2a Interior Earth Structure (left) The Earth’s interior is composed of multiple spherical layers: inner core, outer core, mantle, and a relatively thin crust. (right) The properties of the mantle vary from the brittle lithosphere (part of which is the earth’s crust) to the relatively fluid asthenosphere to the more rigid mesosphere. The denser layers are deeper. (ItO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 3 Figure 3.3 Earth Crustal Configuration The relatively thin oceanic crustal layer and the thicker continental crustal layers “float” on the mantle below…they are said to be isostatic equilibrium. It is their layer thickness differences that cause the continental crust to rise higher out of the mantle relative to the thinner oceanic crust. The different densities of the rock material only make slight differences. The resulting ocean basin depression catches the water that runs off of the land. Note the ~ 20 times (20x) vertical exaggeration of this profile. (ItO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 4 Figure 3.5 Floating Icebergs – An Example The density of the two icebergs is approximately equal, the percentage of the icebergs above the water is also equal. With the one on the left having a larger mass, more water is displaced but also more of the iceberg lies out of the water. (ItO) Figure 3.4 Hydrostatic Equilibrium Any object placed in a fluid displaces a volume of fluid equal in mass to that of the object. When the density of the fluid is greater than that of the object, the volume displaced is less than the volume of the object, causing the difference to float above the surface of the fluid. (ItO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 5 Figure 3.7 A bathymetric profile of the coastal margin. A more detailed picture of the radical changes in ocean depth near the edge of the North Atlantic ocean Basin. The relatively flat regions of the abyssal plain transition into the slightly steeper continental slope region, even steeper continental slope, and finally to the relatively flat and shallow continental shelf region. Note how the vertical exaggeration of the profile help to highlight the different features. (LEiO) Figure 3.6 Ocean Basin Geographic Zones The geographic zones of the North Atlantic are identified in the bird’s eye view of the sea floor above. Below is shown a vertically exaggerated profile of the ocean sea floor features along the transect A-B. (LEiO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 6 Figure 3.8 Plate Movement and Ocean Hazards The Earth’s crust is composed of twelve major plates (named above), whose boundaries are moving as indicated by the orange arrows. Note the regions of plate divergence -usually along mid ocean ridges - and plate convergence -usually associated with ocean trenches. Earthquakes (black dots) silhouette some of these boundaries, with greater concentrations along active convergent zones, and lesser concentrations along active divergent zones. Along with the earthquake hazard is also the possibility of the tsunami hazard. Volcanism is also associated with the earthquake hazard. (ItO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 7 Figure 3.10 Earthquake Hazard Movement along the San Andreas Fault in 1989 (left) caused considerable damage and loss of life in the Oakland/San Francisco area of California (right). (ItO) Figure 3.9 Plate Movement and Earthquakes The San Andreas Fault in California (right) is a transform fault that is actually part of a spreading center in the Pacific that has been “overrun by the expanding North American Plate. Southern and Baja California are moving northward relative to the rest of California. (ItO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 8 Figure 3.11 historical Continental Configurations (top) Pangaea about 200 million years before present (MYBP); (middle) 65 MYBP; and (bottom) present. The movement of the continents is indicated by the arrows. . (?)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 9 Figure 3.12 Present Day plate Configuration Major lithospheric plates and their boundaries. The plates are rigid lithos- (LEiO)10 September late 2007 Lecture 3 Outline – Earth Interior/Bathy 10The Ocean Sea Floor is formedThe Ocean Sea Floor is formedAlong the MidAlong the Mid--Ocean Ridge Spreading CentersOcean Ridge Spreading CentersThe The Ocean Sea Floor Ocean Sea Floor is destroyedis destroyedin the in the Subduction ZonesSubduction