# Constructing a topographic profile

*Practice problems*

Below you will find some sample problems from the geosciences using steps on the constructing a topographic profile page.

**Problem 1:**In Northern California, Lassen Peak forms the centerpiece of Lassen Volcanic National Park (LVNP) - an area of active volcanism that makes up the southernmost volcanic center of the Cascades (volcanoes associated with subduction of the Juan de Fuca plate beneath North America). Besides Lassen Peak, there are lots of other smaller volcanoes scattered around LVNP. One rather interesting one is called Cinder Cone and is a very typical of the smaller volcano type called a cinder cone (hence the name). It has relatively steep sides and a crater at the top. To see the typical profile of a cinder cone, construct a topographic profile along the line A-A' in the map below:

You may wish to download a worksheet with the map and profile (Acrobat (PDF) 2.7MB Jul18 11) to complete this exercise with your pen and paper.

- Sketch in the line on the map or locate the line that is provided.

- Place the edge of a blank piece of paper (or the graph provided) along the line and mark the starting and ending points of the line (label them with A and A', or whatever the given line is labeled).

- Start at one end (maybe it's the A end) and move along the edge of the paper, making a mark on the paper every time a contour line touches the edge of the paper. Make sure you label each mark with the right elevation so that you can transfer that point to the correct elevation on your profile. (If you get tired of marking every elevation contour, you can just label the index (darker) contours and the places where a contour line repeats). You may also want to mark where rivers or streams occur.

- Take note of the highest and lowest elevation you record for later.

- If you have not been provided with a graph for this problem, you need to do the following: When you have marked all of the points where a contour line crosses the paper/profile line, get a piece of graph paper (or a paper with all horizontal lines). Make sure that the graph paper is at least as long as your profile line (you can paste more than one piece together but make sure you line up the grid lines). Draw a horizontal line on the graph paper that is the length of your profile line (label it with A-A' or whatever the line on your plot is labeled). Draw vertical lines above your starting and ending points (these are the y-axes).

- Label the y-axis (vertical lines) with elevations making sure that your scale goes from highest to lowest on your cross-section (see step 3). For example, if your lowest elevation is 4200 feet and your highest elevation is 7600 feet, you might want to label your axis going from 4000 to 8000 feet.

- Line up your tick marked paper with the bottom of the graph and, beginning with the elevation on the left hand side of the paper, go directly up from that tic mark to make a small dot at the corresponding elevation.

- Once you have transferred all of your tick marks to your graph, connect the dots
*with a smooth curve.*

**Problem 2:**

One type of profile that helps geologists visualize topographic data and to understand the topography of rivers is called a **longitudinal profile**. A longitudinal profile allows you to visualize the changing gradient along a river's length. A longitudinal profile is a graph of a river's elevation versus its length. In the Grand Canyon (in Arizona) there are many side canyons with a variety of longitudinal profiles. Let's look at the longitudinal profile of the stream that drains Garces Terrace on the map below. The contour interval on this map is 50 feet. You can download a '

PDF version of this exercise for practice (Acrobat (PDF) 1.1MB Apr10 19).

- Locate the river on the map that is provided.

- Place the edge of a blank piece of paper (or the graph provided) along the line and mark the starting and ending points of the line (label them with A and A', or whatever the given line is labeled).

- Start at one end and move along the edge of the paper, making a mark on the paper every time a contour line touches the edge of the paper. Make sure you label each mark with the right elevation so that you can transfer that point to the correct elevation on your profile. (If you get tired of marking every elevation contour, you can just label the index (darker) contours and the places where a contour line repeats).

- Take note of the highest and lowest elevation you record for later.

- If you have not been provided with a graph for this problem, you need to do the following: When you have marked all of the points where a contour line crosses the paper/profile line, get a piece of graph paper (or a paper with all horizontal lines). Make sure that the graph paper is at least as long as your profile line (you can paste more than one piece together but make sure you line up the grid lines). Draw a horizontal line on the graph paper that is the length of your profile line (label it with A-A' or whatever the line on your plot is labeled). Draw vertical lines above your starting and ending points (these are the y-axes).

- Label the y-axis (vertical lines) with elevations making sure that your scale goes from highest to lowest on your cross-section (see step 3). For example, if your lowest elevation is 4200 feet and your highest elevation is 7600 feet, you might want to label your axis going from 4000 to 8000 feet.

- Line up your tick marked paper with the bottom of the graph and, beginning with the elevation on the left hand side of the paper, go directly up from that tic mark to make a small dot at the corresponding elevation.

- Once you have transferred all of your tick marks to your graph, connect the dots
*with a smooth curve.*