Earth Science - Tuckey Name:                                         
Ice Age Glacial Rebound Activity       / 10 Age:                                             

    When a ship is loaded with cargo, it rides lower in the water (it sinks a little).  When the cargo is unloaded, that same ship will ride higher in the water (it seems to rise up more out of the water).  Similarly, a thick and heavy accumulation of ice (a continental glacier) can cause the crust of the Earth to sink down into the mantle.  If the glacier disappears, then the crust seems to slowly rise up again. 

    The eastern part of Canada around Hudson Bay is a great example of this geological phenomenon.  The area is said to be undergoing glacial rebound.  This rebound is when  land's elevation (measured from sea-level) rises due to the removal of weight that was once on it.  Evidence of rebound comes from finding old beaches or marine fossils at elevations well above sea-level.  At one time, that ground was at sea-level, but now it has risen above it.

    In this map-based activity, you will study the map of eastern Canada provided, and determine the amount of rebound at specific locations.  These locations have been dated carefully with different techniques, and are all as recent as the last Ice Age.

Procedure:

On the map, use colored markers to shade the areas between the contour lines for 10, 30, 50, 70, and 90 meters of rebound.  Do not color areas beyond the contours shown on the map.

  1. What is the value of the highest rebound contour shown?
  2. Relative to Hudson Bay, where are the areas of greatest rebound located?

Use the grid to graph the amount of rebound (in meters) you determined from the map versus the duration of rebound (in years).  The horizontal direction (x-axis) will be the number of years ago, starting with zero on the left side, and the the vertical direction (y-axis) will be the amount of rebound, starting with zero on the bottom.  Complete the graph by drawing a smooth curve as near to as many of the points as possible (sometimes called a "best-fit" curve).  Extend the curve to the origin of the graph (0,0).

  1. The areas on the map with the greatest rebound contours are called rebound centers.  Turn to the map on page 203 of your text and find the locations of the rebound centers identified in Procedure Question 1.  What are these same areas called on the text's map?

  1. What is the probable relationship between the rebound centers and the thickness of the ice in Canada?

  1. What is the probable relationship between the rebound centers and the locations where ice first accumulated?

  1. According to your graph, by what amount did the map area rebound during the first 1000 years shown on the graph (from 6000 to 5000 years ago)?

  1. By what amount has the area rebounded in the last 1000 years?

  1. Has the rate of uplift (rebound) been constant?  Explain.

  1. Which of the following would cause the crust to subside (sink) and which to uplift (rebound)?

a) the formation of a large delta
b) the erosion of a mountain range
c) the formation of a large lake behind a dam
d) the accumulation of sediments in a large sea
e) the building of a skyscraper