Exploring Plate Tectonics w Google Earth - short version (1)

GEOL A110L Introduction to Plate Tectonics via Google Earth Plate tectonics is a unifying framework for understanding the dynamic geology of the Earth. The theory posits that the outermost layers of the Earth (the crust and uppermost mantle) make up the brittle lithosphere of the Earth. The lithosphere is broken up into a number of thin plates , which move on top of the asthenosphere (middle mantle). The asthenosphere is solid but flows plastically over geologic time scales. Plate interiors are relatively stable, and most of the tectonic action (earthquakes, volcanism) takes place where plates meet – where they collide at convergent boundaries , move away from one another at divergent boundaries , or slide past one another at transform boundaries. Reconstructions of the Earth’s tectonic plate locations through time are available, for example, at: http://www-udc.ig.utexas.edu/external/plates/recons.htm#movies http://www.scotese.com/newpage13.htm https://ucmp.berkeley.edu/geology/tectonics.html But how do we define plates and plate boundaries? On what are plate reconstructions and animations based? How do we know plates are moving, how can we track their positions in the past, and how can we predict their positions in the future? To answer these questions, this assignment guides you through an examination of patterns on Earth – the topography of the earth’s surface above sea level, the bathymetry of the ocean floor below sea level, and the distribution of earthquakes and volcanic rock ages. You will then use geologic data to determine long-term average plate motions. To do this, you will use the program Google Earth Pro, and Google Earth layers compiled from various sources. • Getting started with Google Earth Pro (skip if unnecessary) • On your computer, install the latest version of Google Earth Pro from http://earth.google.com/ (if you haven’t already) • Once installed, open Google Earth, under the Tools/Options/3D View/ menu choose the “ Decimal Degrees ” and Meters Kilometers ” options and makes sure the “ Show Terrain ” box is checked. • Open the View menu. Go ahead and experiment with the options, but in general you should just have the Tool Bar , Side Bar and Status Bar checked. Also on the View menu, hover over Navigation and you will see several options for the compass arrow and slide bars in the upper right corner of the Google Earth screen. “ Automatically ” is a good choice as it leaves a ghost of the image visible until you hover over it. • Load the DynamicEarth.kmz file into GE (download from Canvas). You should be able to double-click on the filename and it will open within GE. Or, you can download the file onto your computer, and open it in GE by using File/Open and navigating to the file.

Once the DynamicEarth.kmz is loaded, click and drag to move it from “Temporary Places” to “My Places.” Then save “My Places” by clicking File/Save/Save My Places. DynamicEarth.kmz will now be available every time you open GE on this particular computer. When you exit, GE should save “My Places” for the next time. Ok, with an active Internet connection, you now have an interactive view of the earth! Take some time to explore the Earth with Google Earth and figure out how the navigation works using the keyboard, your touch pad, your mouse. For example:  Zoom in and out, move N, S, E, W, grab and spin the globe, etc. The resolution will change as you zoom. Clicking on the “N” of the navigation compass reorients the view so north is “up.”  At top left, “search” (and fly to) any place of interest. Zoom in and click on the “street view” icon (orange stick figure under the compass at top right) to explore an area as if you were on foot  Zoom in to see individual buildings, roads, cars, etc.  Go 3D - zoom into a significant topographic feature (e.g. Mount Everest, the Grand Canyon, Niagara Falls). Hold the Shift key down and tilt the terrain using the Up/Down arrows to tilt the terrain, and spin the terrain using the Right/Left buttons. Do the same thing for topographic features on the ocean floor. Note that under Tools/Options/3D View you can increase the vertical exaggeration by up to 3x. This is useful to emphasize subtle features but is pretty scary when you look at the Grand Canyon that way!  On the Google Earth tool bar, click the clock-with-an-arrow icon to explore historical imagery in an area of interest (views through time of the Orange Coast College campus, for example)  By clicking and dragging, you can move things that you have found and want to save, from the “Search” menu into “My Places.” You can also re-organize “My Places” by adding and deleting items, changing the order of things, making subfolders, etc.  Explore the built-in items under the Layers menu at bottom left, and Dynamic Earth layers in your Places menu. Expand and contract the folders and subfolders, turn various items on and off, etc. For example, with the Dynamic Earth/ Volcanoes of the World layer displayed, right-clicking on a volcano brings up an information box about it. • Plate motion Motion across the mid-Atlantic ridge: the South American plate vs. the African plate Turn on the “Seafloor age” and the “Plate Boundary” layers. The “Seafloor age” layer shows the ages of volcanic rocks that have erupted and cooled to form the ocean floor. Focus on the Atlantic Ocean. Note that the age bands generally run parallel to the spreading ridges. Seafloor age is a critical piece of evidence for plate tectonics; these are used to reconstruct how ocean basins have developed over time and predict how they may evolve in the future.

fall exactly on the line; if R 2 =0 there is no significant linear trend.) Attach/upload the chart with your completed lab activity. unable to graph, had a hard time figuring out the calculations that were needed and how to document! • Describe the motion of your chosen plate relative to the mid-Atlantic ridge, based on this seafloor age data – the direction of motion, the average speed (slope of the best fit line) and whether or not speed and direction has been constant over time. Report your answer in cm/year – you will likely need to convert your units from your graph to do this! (See Lab 1) • Compare these results to an independent data from the Tristan da Cunha Volcanic Island/Seamount chain on the African plate off the southwest coast of Africa as follows: To access this data, expand the “Volcanic chain (“hot spot” tracks) layer on GE, then expand the AtlanticOceanChains layer, and then click to display Tristan da Cunha. You may need to click off Sea Floor age layer to view the hot spot data (you can toggle layers on and off to compare the datasets). These islands and seamounts are volcanic edifices built up on older seafloor, formed by eruption of magma from relatively stationary sources (“hot spots”) underneath the moving plates. The numbers are the radiometric ages in millions of years of volcanic rocks collected from each island/seamount. Does data from the Tristan da Cunha Volcanic Island/Seamount chain support the plate motion you deduced from the sea floor age data? Explain. Apply what you have learned – the Pacific Plate • Turn your attention to the Pacific plate. Note that the Pacific Ocean is comprised of several plates; we want to focus on the very large Pacific plate (not the Nazca plate, or Cocos plate, or Philippine plate or other plates.) The Pacific plate is “born” underwater at the East Pacific rise, the spreading ridge west of South America. It is being destroyed at convergent boundaries around its northern, western, and southern boundaries. • Is the East Pacific Rise spreading faster or slower than the mid-Atlantic

Ridge and how can you tell - without doing any calculations? Has the rate been constant over time? - - Yes, the East Pacific rise is moving at a faster velocity than the Mid-atlantic ridge. we can know this by simply seeing the arrangement of both spreading centers. • Make and print out a graph (like what you did in question 7) for movement of the Pacific plate away from the East Pacific Rise. Attach/upload the chart with your completed lab activity. • Describe the motion of the Pacific plate relative to the East Pacific Rise, based on this seafloor age data - direction of motion, average speed and whether speed and direction has been constant over time. - The motion of the Pacific plate occurs away from the East Pacific rise as from there the spreading occurs. That's why the youngest crust for the Pacific plate will be found near the East Pacific rise side and as we go away from rise the age will increase. • Consider the Volcanic Chains in the Pacific Ocean (Hawaiian/Emperor, Louisville, and Easter Island). Do these data support the movement you deduce for the Pacific Plate? Explain. - Pacific plate is moving away from the east pacific rise in the northwest direction and so, the youngest crust lies close to the ridge and age increrases away from the ridge. • What does the bend in the Hawaiian/Emperor chain indicate happened about 50 million years ago to the direction of Pacific plate movement? - Some sort of collision took place