How Long Does it Take?
Grades: 5 - 12
Duration: 50 minutes
Goals:
- Students will appreciate the slow movement of glaciers.
- Students will understand the danger posed by crevasses to glacier travel.
- Students will understand the relationship between time, distance and rate.
Objective:
Students will determine the time required for a crevasse "victim" to emerge out the front of a moving glacier.
Materials for each group of three students:
- Topographic map of a region of Alaska containing glaciers with a scale of 1: 50,000. Each group of three students should get the same map
- One meter piece of light weight string
- Calculator
Background:
In this lesson, students determine how long it will take an item lost in a crevasse to emerge out the front of a glacier. Students need to know that glaciers move, what crevasses are and that crevasses move with the glacier that contains them. Students can be told that crevasses open and close as the glacier moves. This lesson is based on an actual historical event.
Procedure:
Tell the class the following story: In the 1800's a man, walking on a glacier in Switzerland, fell into a crevasse and died. A glacialogist familiar with that glacier predicted the man's body would emerge from the front of the glacier on a specific day during a specific month and year many years later. Everyone forgot about the prediction, but low-and-behold the man's body did come out the front of the glacier and the records showed it was the same month and year of the glacialogist's prediction!
Tell the class to imagine a girl, Sarah, walking on a glacier on the map you have chosen and further, that she is walking at a specific spot on the map. (You may select any spot on the glacier but must tell the class where that location is on the map.) Sarah has dropped a beanie-baby - or whatever the current rage toy is - in a crevasse at that point. Sarah wants to determine how long it will take for the beanie-baby to emerge from the front of the glacier to decide if it is worth it to come back and get the beanie-baby at that time.
Form students into groups of three.
Ask the class what Sarah needs to know in order to solve this problem.
Let the class think about it and discuss it among their groups a few minutes.
Sarah needs to know:
- The average rate of movement of the glacier.
- The distance between the crevasse containing her beanie-baby and the front terminus of the glacier.
- Lay the string down on the map to follow the course of the glacier from Sarah's location to the glacier terminus. The string does not have to be straight.
- Pick up the string, pull it straight, and compare it to the distance scale at the bottom of the map.
- If the distance is 4.7 km - just a random distance - this is 4,700 meters.
- With a rate of movement of 100 meters per year this would be:
- Satisfactory student participation and cooperation within their groups.
- Subjective determination of this = 0 - 5 points.
- Correct answer to Sarah's problem from student group, i.e., 47 years = 5 points.
- Two points off for: incorrect number, incorrect or missing units.
Tell the class the glacier is moving 100 meters per year - not unreasonable. Tell the class to use the scale at the bottom of the map and the piece of string to determine the distance from the crevasse to the glacier terminus. Ask the class to work in their groups and discuss with other groups to try to figure out if Sarah should wait until the beanie-baby comes out the front - terminus - of the glacier. Circulate throughout the class giving assistance through Socratic questioning of the students.
Problem Solution:
Answer: Sarah would need to wait 47 years for her beanie-baby to come out the front of the glacier. She should probably find something else to do during that time.
Evaluation:
