Name ____________________________________________ Period _______ Date _______________
Ocean Tides and Tidal Ranges
For most coastal location, high tides and low tides follow each other in a regular pattern. The level of water at each high tide
and at each low tide however varies from day to day and from location to location. In the same way, the difference in water
level between high tide and low tide, called tidal range, is constantly changing. The greatest tidal ranges occur near the times
of the new moon and the full moon and the full moon and are called spring tides. The smallest tidal ranges occur near the
times of the quarter moon phases and are called neap tides.
Another factor that influences tidal range is the shape of the bay in which the tide occurs. Bays that become narrower away
from the ocean cause the water level to rise higher as the tide moves into the bay. Such bays tend to have a large tidal range.
On the other hand, bays that widen away from their mouths allow the water to spread out. These bays tend to have small tidal
ranges. This activity examines the tides at three locations: Boston, Massachusetts, on Boston Harbor and Saint John, New
Brunswick, on the Bay of Fundy.
Procedures
1. The upper table on the next page contains sample data for spring and neap tides for the Boston area. Choose a colored
pencil and plot the data for both tides on the grid. Connect the points with a smooth curve.
2. The lower table on the next page contains sample data for spring and neap tides for the Saint John Bay area. Choose a
colored pencil and plot the data for both tides on the grid. Connect the points with a smooth curve.
Data Tables
Boston, MA
Spring Tide Data
Time (hour)
0
1
2
3
4
5
6
7
8
9
10
11
12
Neap Tide Data
Water Level (m)
2.4
3.1
3.5
3.4
3.0
2.3
1.4
0.5
-0.2
-0.3
0.0
0.6
1.4
Time (hour)
0
1
2
3
4
5
6
7
8
9
10
11
12
Water Level (m)
1.6
2.1
2.5
2.5
2.3
2.0
1.5
1.0
0.6
0.6
0.8
1.2
1.7
Saint John, NB
Spring Tide Data
Time (hour)
0
1
2
3
4
5
6
7
8
9
10
11
12
Water Level (m)
4.5
6.3
7.7
8.2
7.8
6.7
5.1
3.2
1.5
0.5
0.7
1.6
3.2
Neap Tide Data
Time (hour)
0
1
2
3
4
5
6
7
8
9
10
11
12
Water Level (m)
4.5
5.6
6.3
6.5
6.2
5.4
4.4
3.3
2.5
2.2
2.5
3.3
4.4
Analysis and Conclusions
1. Assume you are standing in the classroom that has a height of 2.5 meters. Imagine that the floor of the classroom
represents the lowest water level for the spring tide. Relative to yourself and to the room’s ceiling, where would the
highest water level occur for each of the two locations? Would these water levels change for neap tide?
2.
Order the two locations of Boston and Saint John from the greatest to the smallest tidal range.
3.
How do the maximum water level values on your graphs compare for the spring and neap tides?
4.
Use your notes to compare the alignment of Earth, the Sun, and the Moon for spring tides and neap tides.
5.
Even though the water levels of these locations change drastically, the percentage by which the tidal range decreases
from spring tide to neap tide is about the same for all three locations. Why do you suppose this is true
6.
Based on your graphs, how long would you expect the interval between high tides to be for each of the two locations?
7.
Saint John is located on a long, narrow bay that is cut off from the Atlantic Ocean, while Boston is located on a
relatively wide harbor that opens into the Atlantic Ocean. How do these facts help explain the difference in tidal
ranges for Boston and Saint John?