CHAPTER 24: OCEAN TIDES AND TIDAL RANGES LAB INVESTIGATION
Learning Targets
 Plot and graph tide data for three different locations
 Compare & analyze data for tides at three different locations
Background Information:
For most coastal locations, high tides and low tides follow each other in a regular pattern. The level of the 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 the tidal range, is constantly changing. The greatest
tidal ranges occur near the times of the new moon and the full moon when the sun, moon and earth are aligned. They
are called spring tides. The smallest tidal ranges occur near the times of the quarter moon phases where the moon and
sun are at right angles to the Earth. They are called neap tides.
Another factor that influences tidal range is the shape of the bay in which the tide occurs. Bays that narrow 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.
Bays that have narrow openings to the ocean and remain narrow also tend to have a large tidal range because the water
is more compressed as it travels up the bay and are more exaggerated. On the other hand, bays that widen away from
their entrance tend to have small tidal ranges. The last factor that influences tides is the size of the body of water. The
moon’s pull has a greater effect on large bodies of water. For example, the Great Lakes do not experience high and low
tide because they contain a small mass of water compared an ocean.
Procedures – This activity examines the tides at three locations:
Bay
Location
Water Body Shape
Boston Harbor
Boston, Massachusetts
Wide opening into Atlantic, narrows away from the ocean
Bay of Fundy
Saint John,
New Brunswick
Narrow opening into Atlantic and remains narrow
Mobile Bay
Mobile, Alabama
Narrow opening into the Gulf of Mexico, widens away from the Gulf
1. The tables on the next page contain data for the spring and neap tides for the three different locations.
Find the tide data for Boston at spring/neap tide. Choose one color to plot the data for the spring tide
and another color to plot the data for neap tide on the Spring and Neap Tide at Boston, MA graph.
Connect each point with a smooth line curve in the chosen color. Include a color-code key.
2. Using the same colored code, plot the data for both the spring tides and neap tides on the Spring and
Neap Tide Saint John and Mobile graphs. Notice that the water level scale changes!! Connect each
point with a smooth line curve.
3. Answer the Analysis and Conclusion questions after graphs are complete.
Spring & Neap Tide Data Tables
Time
(hour)
0
2
4
6
8
10
12
14
16
18
20
22
24
Time
(hour)
0
2
4
6
8
10
12
14
16
18
20
22
24
BOSTON, MA
Spring Tide Neap Tide
Water Level Water Level
(m)
(m)
2.4
3.5
3.4
1.4
-0.2
-0.2
1.4
3.1
3.1
1.7
0.5
-0.3
0.6
1.6
2.3
2.3
1.5
0.8
0.8
1.7
2.1
2.1
2.0
1.0
0.6
1.2
Time
(hour)
SAINT JOHN, NB
Spring Tide Neap Tide
Water Level Water Level
0
2
4
6
8
10
12
14
16
18
20
22
24
(m)
(m)
4.5
7.7
7.8
5.1
1.5
1.5
4.0
7.5
7.5
5.6
3.2
0.5
1.6
4.5
6.3
6.2
4.4
2.5
2.5
4.4
5.9
6.1
4.2
3.2
2.2
3.3
MOBILE, AL
Spring Tide Neap Tide
Water Level Water Level
(m)
(m)
0.43
0.53
0.54
0.45
0.3
0.12
-0.02
-0.10
-0.12
-0.08
0.03
0.18
0.34
0.31
0.36
0.37
0.32
0.23
0.14
0.06
0.03
0.03
0.06
0.13
0.22
0.31
Saint John, NB
Boston, MA
Mobile, AL
Analysis and Conclusions:
**Base your answers on the graphs and the information found in the introduction.**
1. How does the maximum water level for spring tides compare with the maximum water level for neap tides?
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2. How are the Earth, the Sun, and the Moon aligned during spring tide? How are they aligned during neap tide?
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3) Calculate the Tidal Range during Spring Tide for each location:
— The Tidal Range is the difference in water level between high tide and low tide.
(So take the highest water level minus the lowest water level. Careful with the negative numbers!)
2
Bay
Boston Harbor
Bay of Fundy
Mobile Bay
Location
Boston,
Massachusetts
Saint John,
New Brunswick
Tidal Range (m)
Mobile, Alabama
4) If you calculated the tidal range for neap tide would it be higher or lower than the spring tide tidal range? Why?
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Lab Activity Laboratory Manual
5) How does the alignment of the Earth, Sun and Moon affect the tidal range?
________________________________________________________________________________________________
6) Which location has the greatest tidal range? ____________________ the smallest tidal range? __________________
7) Both Boston Harbor and the Bay of Fundy are located on the Atlantic ocean. Explain why the Bay of Fundy has a
greater tidal range.
________________________________________________________________________________________________
________________________________________________________________________________________________
8) Mobile Bay is located in the Gulf of Mexico. Boston Harbor and the Bay of Fundy open into the Atlantic Ocean. Why
does Mobile Bay have such a small tidal range?
________________________________________________________________________________________________
________________________________________________________________________________________________
9) Based on your graphs: How long is the interval between high tides in Boston? ________________________________
How long is the interval between high tides in Saint John? ______________________________
How long is the interval between high tides in Mobile? _________________________________
10) How many high tides per day (24hrs) occur in Boston? _________ Saint John? __________ Mobile? __________
Explain the reason for the differences: __________________________________________________________________
________________________________________________________________________________________________
Name: _________________________________________
Date: _______________
Block: _______