Are You in a Hotspot? A map-reading activity in recognizing tectonic settings. Students will work through a series of quantitative and visual exercises to: 1.Review map reading skills. 2.Discern key features of hotspots and island arc systems Prepared for MARGINS and SSAC by: Judy Harden – University of South Florida © The Washington Center for Improving the Quality of Undergraduate Education. All rights reserved Core Quantitative Skills basic math SSAC2007.QE511.JAH1.2 1 Supporting Quantitative Issues unit conversion scale vertical exaggeration The maps used in this module were created with GeoMapApp and/or Google Earth. Both are free downloads. GeoMapApp Google Earth

2 You have heard or read about plate tectonics and the three different types of plate margins: convergent, divergent, and transform. You have also heard of intraplate hotspots. This module allows you to apply the knowledge you have gained to differentiate between hotspot island chains and volcanic island arc systems. You will travel to two exotic places and begin your journey with an exercise in map reading.plate tectonics Slides 3 and 4 present questions, a spreadsheet, and a map and addresses general map-reading skills. Slides 5 explains map scale and vertical exaggeration. Slides 6 and 7 present questions, a spreadsheet, and a map regarding vertical exaggeration and elevation profiles. Slides 8 and 9 ask you about elevation differences and volcanism in the map area. Slides present a new map area with questions similar to those on Slides 3-8. Slides 15 and 16 ask you to make distinctions between the two study areas. Slide 17 presents end of the module questions and a template for the spreadsheet exercises. Slide 18 (instructor version) gives suggestions for pre-test questions. Slide 19 consists of questions. Slides (instructor version) are supplemental maps that can be used to make adaptations to the exercise. Overview of Module If you are not already viewing this in “Slide Show”, do so now!

3 Investigation 1 – Study Area 1 The computer-generated, digital bathymetric map on the following slide shows islands and seamounts. Answer the following questions about the map: 1.In which hemisphere is this area? 2.Using the color scale on the left of the map, how many features are above sea level? 3.What is the range of longitude on the map? Latitude? 4.How many degrees longitude are represented by the map? Latitude? 5.Using the bar scale, what is the total area in square kilometers? Convert to m 2, mi 2 and ft 2. If you see ##### in Cells D9 and F9, highlight the cell. Go to Format  Cells  and choose “scientific”. = cell with a number in it = cell with a formula in it You will be using this spreadsheet again, so be sure to enter formulas into the orange cells that get the same answers as shown. Be sure you understand how to read the map to determine the numbers in the yellow cells. You will need to find values like these on a map in a future slide. If you entered the correct formulas in the orange cells, your numbers should match those in the spreadsheet. Use the template provided on Slide 17 to recreate this spreadsheet and to answer the questions above.Slide 17

4 Investigation 1 - This digital bathymetric map depicts a chain of volcanic island. Each elevated feature is a volcano. The detail shown in this highlighted area to the left and the other areas indicated by the arrows is from seismic profiles collected on scientific cruises. 4

5 Map Scale and Vertical Exaggeration Elevation profiles show variations in topography or bathymetry. Vertical exaggeration (VE) is often used to bring out subtle topographic features. It is also used for profiles that cover large horizontal distances (kilometers) relative to the relief (meters). Vertical exaggeration simply means that the vertical scale is larger than the horizontal scale. If the scale is 1:24,000, it means that one of ANY unit on the map is equal to 24,000 of the same unit on the Earth’s surface. Scale is a ratio and can be written as: Maps represent a portion of the Earth’s surface. All maps have a scale to indicate the relationship between the distance on the map and the distance on the Earth. Where l m is distance on the map, and l E is distance on the Earth. If the vertical scale is 1:100 and the horizontal scale is 1:1,000 the vertical scale is larger than the horizontal scale.

6 Investigation 2 – Study Area 1 Study the image on the next slide. Answer the following questions about the elevation profile: 1.How many features along the profile are above sea level? 2.Is the profile vertically exaggerated? By how much? (use spreadsheet below) 3.What are the units for vertical exaggeration (VE)? 4.What is the approximate elevation in the profile for each of the subaerial features from A to A’? 5.What is the largest depth shown to the seafloor? 6.Using the approximate value you gave for the volcano closest to A’ (Question 3) and the largest depth to the seafloor (Question 4), what percentage of the volcano’s relief is subaerial? Recreate this spreadsheet to answer Questions 2 and 6. Be sure you understand how to find the numbers in the yellow cells from the profile. You will need to find similar values on a map in a future slide. Note Units Vertical exaggeration or map scaleVertical exaggeration or map scale help.

7 Investigation 2 – This profile shows the elevation along the line indicated on the map. A A’ A The broken line for this feature reflects the lack of some topographic data (gray areas on the map). 6

8 Investigation 3 – Study Area 1 1.Although it is not possible to get a profile through the center of each volcano with one line, what general statement can you make about the variation in elevation from A’ to A? 2.What can you infer about the ages of the islands from A’ to A (think about erosion)? 3.What can you say about the directional trend of the island chain? A A’ A

9 Investigation 4 – Study Area 1 The orange volcano-shaped symbols denote historically active volcanoes. Below is a GeoMapApp relief image of the same island chain overlain on Google Earth’s rendition of the area.GeoMapAppGoogle Earth 1.Do you see any evidence of an ocean trench alongside the island chain? Where should you look? 2.How would you describe the location of active volcanism along this island chain?

10 Investigation 5 – Study Area 2 The computer-generated, digital bathymetric map on the following slide shows islands and seamounts. Answer the following questions about the map: 1.What hemisphere is this area in? 2.Using the color scale on the right of the map, how many of the features are above sea level? 3.What is different about the area below sea level from that of the previous study area? 4.What is the range of longitude on the map? Latitude? 5.How many degrees longitude are represented by the map? Latitude? 6.Using the bar scale, what is the total area in square kilometers? Convert to m 2, mi 2 and ft 2. If you get ##### in Cells C9,D9 and/or F9, highlight the cell. Go to Format  Cells  and choose “scientific”. = cell with a number in it = cell with a formula in it Use the spreadsheet you created for Investigation 1. Replace the values in the yellow cells, and the correct answers will appear in the orange cells (if your cell formulas are correct).

11 Investigation 5 – The red rectangle outlines a volcanic island chain. Each elevated feature is a volcano. 10

12 Investigation 6 – Study Area 2 An elevation profile and map are shown on the next slide. Study the image on the next slide. Answer the following questions about the elevation profile: 1.How many features along the profile are above sea level? 2.Is the profile vertically exaggerated? By how much? (use spreadsheet below) 3.What is the approximate elevation in the profile for each of the subaerial features from A to A’? 4.What is the largest depth shown to the seafloor? 5.Using the approximate value you gave for the volcano closest to A’ (Question 3) and the largest depth to the seafloor (Question 4), what percentage of the volcano’s relief is subaerial? Use the spreadsheet you created for Investigation 2. Replace the values in the yellow cells, and the correct answers will appear in the orange cells (if your cell formulas are correct).

13 Investigation 6 A A’ 12 A A’

14 Investigation 7 – Study Area 2 1.What is represented by the dark blue area crossed by the profile? 2.What is the deepest point along the profile? 3.What is the distance from the volcano (near A on the profile) to the deepest point? 4.How would you describe the distribution of historically active volcanoes in this map area? A A’ A

15 Investigation 8 – Study Area 1 Using the information presented in the investigations and maps A and B (below, Study Area 1) and maps C and D (next slide, Study Area 2): 1.Describe the tectonic environment (convergent, divergent, transform or intraplate) of the two study areas. Justify your answer. 2.Describe the direction of plate motion for each study area. 3.Which set of maps (Study Area 1 or Study Area 2) would be easier to use to calculate the rate of plate motion? 4.What information would you need to calculate the rate of plate motion? Map A Map B Map A shows historically active volcanoes and their names for study area 1. Map B shows all earthquakes (maroon circles) >1 magnitude for the years (21 total earthquakes). Earthquake data obtained from:

16 Investigation 8 - Study Area 2 Map C shows historically active volcanoes and their names for Study Area 2. Map C Map D Map D shows all earthquakes (maroon circles) >1 magnitude for the year 2006 only! (811 earthquakes) Earthquake data obtained from:

17 Turn in one Excel spreadsheet similar to the one shown to the right, answering all of the questions in each of the investigations and the end of the module questions on the next slide. End of Module Assignment You can use the spreadsheet to the right as a template by double clicking on it (in “normal” view, not slide show). The spreadsheet will open up in Excel format. Click on the top left cell and drag the mouse down to the bottom right, highlighting cells A1 through F109. Right click on the highlighted information and select copy. Open up Excel and paste into the top left cell. Back to Slide 3

18 1.How many degrees latitude are represented on a map from 35° 30’ to 42°? 2.If one inch on the horizontal scale of a map represents 10 km and one inch on the vertical scale represents 1000 m what is the vertical exaggeration? 3.You are looking at two different maps, one with a scale of 1:24,000 and one with a scale of 1:250,000. Which map has the larger scale? 4.If a map shows an area of 200 km by 30 km, what is the total area of the map? 5.What percentage of a volcanic island’s relief is above sea level if its elevation above sea level is 1200 ft and its elevation below sea level is 2400 ft? 6.If the distance between two islands is 27 km, how many miles separate the islands? End of Module Questions