Welcome Geology Students!

Finding yourself on a topographic map #1

Navigating Topographic Map #1

Goal

Background on Mt. Cleveland

Position with triangulation

What to turn in and how

Introduction

Geologists use topographic maps. Geologic maps are often made on topographic base maps. That is, the geology and geologic features are plotted on a contour map of the topography. So, it is is critical for geologists to understand how to use topographic maps. In the next couple of exercises we will use topographic maps and information to locate points on the map and to infer features about Mt. Cleveland volcano and its neighbors. This exercise involves triangulation using compass bearings.

Mt. Cleveland volcano

Mount Cleveland is a volcano in the Aleutian Islands, an archipelago that extends west from the Alaska mainland.The Aleutians are a volcanic arc, formed from the subduction of the Pacific Plate beneath the North American plate. Volcanoes form the arc, that stretches hundreds of kilometers across the northern Pacific.

Mt. Cleveland is one of the most active volcanoes in North America. It is monitored by the Alaska Volcano Observatory (AVO), which is operated by the U.S. geological Survey and the University of Alaska.

Get to know Mt Cleveland

Use Google Earth Pro to locate Mount Cleveland in the Aleutian arc. Notice its position along the arc and note that it is part of a group of volcanoes that form four islands.

Check out the live webcam that AVO has set up to monitor Mt. Cleveland. if it is cloudy or dark, you can check out their "Clear day image" on the same page.

Check out the Smithsonian webpage about Mt Cleveland and its recent history

Obviously, Mt Cleveland is an active volcano and needs to be monitored. In summer months it is visited by volcano scientists to monitor the volcano and to understand its volcanic history.

Let's consider a team going to monitor Mt. Cleveland...

Map position by triangulation

The team is dropped off by helicopter. After unloading they decide to locate their position. It is clear enough (remarkably!) to see three volcanic peaks in the distance. These are: (1) the symmetric and tall peak of Mt Cleveland, (2) the more distant and truncated peak of Herbert volcano to the left of Mt Cleveland, and the hazy peak of another volcano to the right (north) of Mt. Cleveland.

the view
The (blurry!) view from the landing zone webcam. Mount Cleveland is the center of the three volcanoes. Herbert volcano is to the left.

Now look at the topographic map. Mount Cleveland and Herbert volcano are labeled. The third volcano island NW of Mount Cleveland is not named on the map. The contour interval on the map is 100 m, Mt. Cleveland rises from sealevel to 1730 m (approximately, its height changes with nearly every eruption).

Using the photograph and the map, guess the location of the helicopter drop zone. Consider the relative locations of the three volcanic peaks in the photo from the webcam at the drop zone and the positions of these three peaks on the map.

Your guess might be quite accurate, or you might be off! Improve your guess using bearings to triangulate your location. With a Brunton compass, team members "shoot" bearings from your location to three points. These three points are:

  1. Mt Cleveland summit: 287$^{\circ}$
  2. Herbert volcano east crater rim: 262$^{\circ}$
  3. Unnamed volcano summit (NW of Mt Cleveland): 299$^{\circ}$

To triangulate the team's position, find the three points on the map. Use the azimuth tool to find the bearing from the point to the team's location. Hint: You will have to subtract 180$^{\circ}$ from the bearing measured from the team's location to the point. The bearing lines intersect at the team's location.

Drag the red circle to move the azimuth tool

Drag the blue circle to change the bearing

read the azimuth (the blue number)

Extra construction lines are OK. But if you make too many just start over by refreshing (reloading) the webpage.

Save the image by right-clicking on the image.

Answer these questions

Make a word document that contains this work:

  1. A *.png image (file) of the map showing the location of the team in the helicopter zone. Remember, right click the mouse over the map to save the file.
  2. What bearing would the team sail to go from the helicopter landing zone to the north beach on the Herbert volcano island?
  3. A team member hikes up the north side of Herbert volcano and stands on the north rim of the crater. What is the bearing to the summit of Mt. Cleveland?
  4. Turn in the word document.