Tide Notes
terms: spring tide, neap tide, flood tide,ebb tide,
slack tide, mean low water, mean high water, sea
level, diurnal tides, semidiurnal tides
http://www.iit.edu/~johnsonp/smart00/lesson4.htm#highest
http://www.alternative-energy-news.info/seagen-tidal-stream-turbine/ TIDAL POWER!
Where are the highest tides in the world?
The Guinness Book of World Records states the world's highest tides to be in the
Minas Basin, NS, with the maximum tidal range recorded at 16.8 meters (54.6
ft). Parrsboro, the largest Seaport on the Minas Basin, affords the best view of
this tidal phenomenon. At this point the tide floods and ebbs over 3.2 kilometers
(2 mi.) of tidal flat from the low watery mark to the head of the harbor. Each
phase of the cycle takes approximately 5hrs\40 min. which results in each
succeeding high or low water mark range an average 14m. (45.5 ft.) while the
harbor heights are about 7.5 m (24 ft.). For more details see the websites
http://museum.gov.ns.ca/fossils/protect/tides.htm and
http://www.valleyweb.com/fundytides/.
Tide Amplitudes Around the World
Place
Portland ME
Boston MA
NYC
Savannah GA
Key West FL
Galveston TX
San Diego CA
San Francisco CA
Seattle WA
Cordova AK
Honolulu HI
Average Tidal Range in Meters
2.7
2.9
1.4
2.2
.4
.4
1.2
1.2
2.3
3.0
.4
http://www.laurencenet.net/Fundy.html
http://www.paulillsley.com/timelapse/index.html
TIME LAPSE VIDEO BAY OF FUNDY
The Canadian Press
http://oceanservice.noaa.gov/education/yos/resource/JetStream/ocean/fundy_max.htm
The tide generating forces act on every particle of the Earth
but only the water is free to move. Thus on the side of the
Earth nearer the Sun or Moon, gravitational attraction of the
Sun/Moon combines with the centrifugal force of the Earth
and the water tends to pile up and cause a high water at
position "a", as shown in Fig. A. On the opposite side of the
Earth, centrifugal force is greater than the gravitational
attraction and tends to cause another high at "b". At the
meridian pp' the tendency is for low water to be caused.
Figure A
The Earth makes one complete revolution about its axis in
an average of 24 hours, so that any position on the Earth is
in direct line with the Sun every 24 hours. The interval
between successive high waters caused by the solar tidegenerating effect is thus on an average 12 hours.
Because of the Moon's movement in space any position on
the Earth is in direct line with the Moon once every lunar
day, which is on average about 24 hours 50 minutes. The
interval between successive high waters caused by the lunar
tide-generating force is thus on average 12 hours 25
minutes.
SPRING TIDE
Approximately 15 days later, at the full Moon, the Earth is between the Sun and Moon as
shown in Fig. D and the Moon and Sun are acting in opposition.
SPRING TIDE
NEAP TIDE
•Every place on Earth passes through these points, called high tides, twice
per day as the Earth rotates.
•High tides occur every 12 hours 25minutes
–remember, the Moon moves!
•The Sun’s tidal effect on Earth is not as strong.
–the ratio Earth’s diameter : distance to Sun is much less than ratio Earth’s diameter :
distance to Moon
What are the different types of Tides
When the sun and moon are aligned, there are
exceptionally strong gravitational forces, causing very
high and very low tides which are called spring tides,
though they have nothing to do with the season. When
the sun and moon are not aligned, the gravitational
forces cancel each other out, and the tides are not as
dramatically high and low. These are called neap tides.
Spring Tides
When the moon is full or new, the gravitational pull of the moon and sun are
combined. At these times, the high tides are very high and the low tides are very
low. This is known as a spring high tide. Spring tides are especially strong tides
(they do not have anything to do with the season Spring). They occur when the
Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon
and the Sun both contribute to the tides. Spring tides occur during the full
moon and the new moon
Neap Tides
During the moon's quarter phases the sun and moon work at right angles,
causing the bulges to cancel each other. The result is a smaller difference
between high and low tides and is known as a neap tide. Neap tides are
especially weak tides. They occur when the gravitational forces of the Moon and
the Sun are perpendicular to one another (with respect to the Earth). Neap tides
occur during quarter moons.
•This fight between Moon’s pull & Earth’s rotation
causes friction.
•Earth’s rotation slows down (1 sec every 50,000 yrs.)
Synchronous Rotation
•…is when the rotation period of a moon, planet,
or star equals its orbital period about another
object.
•Tidal friction on the Moon (caused by Earth) has
slowed its rotation down to a period of one
month.
•The Moon now rotates synchronously.
–We always see the same side of the Moon.
•Tidal friction on the Moon has ceased since its
tidal bulges are always aligned with Earth.
A FEW FACTS ABOUT LUNAR TIDES
The gravitational force of the moon is one ten-millionth that of earth, but
when you combine other forces such as the earth's centrifugal force
created by its spin, you get tides.
The sun's gravitational force on the earth is only 46 percent that of the
moon. Making the moon the single most important factor for the creation of
tides.
The sun's gravity also produces tides. But since the forces are smaller, as
compared to the moon, the effects are greatly decreased.
Tides are not caused by the direct pull of the moon's gravity. The moon is
pulling upwards on the water while the earth is pulling downward. Slight
advantage to the moon and thus we have tides.
Whenever the Moon, Earth and Sun are aligned, the gravitational pull of the
sun adds to that of the moon causing maximum tides.
Spring tides happen when the sun and moon are on the same side of the
earth (New Moon) or when the sun and moon are on opposite sides of the
earth (Full Moon).
When the Moon is at first quarter or last quarter phase (meaning that it is
located at right angles to the Earth-Sun line), the Sun and Moon interfere
with each other in producing tidal bulges and tides are generally weaker;
these are called neap tides.
Spring tides and neap tide levels are about 20% higher or lower than
average.
Offshore, in the deep ocean, the difference in tides is usually less than 1.6
feet
The surf grows when it approaches a beach, and the tide increases. In bays
and estuaries, this effect is amplified. (In the Bay of Fundy, tides have a
range of 44.6 ft.)
The highest tides in the world are at the Bay of Fundy in Nova Scotia,
Canada.
Because the earth rotates on its axis the moon completes one orbit in our
sky every 25 hours (Not to be confused with moon's 27 day orbit around
the earth), we get two tidal peaks as well as two tidal troughs. These events
are separated by about 12 hours.
Since the moon moves around the Earth, it is not always in the same place
at the same time each day. So, each day, the times for high and low tides
change by 50 minutes.
The type of gravitational force that causes tides is know as "Tractive"
force.
Tidal Differences Table
PLACE
TIDAL DIFFERENCES
Time (hrs.:mins.) Height (ft.)
HW
LW
HW
LW
York River
Tues Marshes Light
–0:09
Gloucester Point
+0:16
Yorktown
+0:07
West Point
+2:03
James River
Mulberry Point
+1:56
Hog Point
+2:11
Jamestown Island
+2:54
Outer Coast of Virginia
Virginia Beach
–1:30
Chesapeake Bay Eastern Shore
Onancock
+2:52
Fisherman’s Island
–0:47
–0:07
+0:07
+0:01
+2:28
–0.3
–0.1
–0.1
+0.3
0.0
0.0
0.0
0.0
+2:16
+2:28
+3:26
–0.1
–0.4
–0.5
0.0
0.0
0.0
–1:35
+0.9
0.0
+3:09
–1:00
–0.7
+0.5
0.0
0.0
Telling Tides Worksheet
Name:
Class:
Date:
Procedure
1.
Enter the date and location.
2.
In the “Hampton Roads” column, enter the times and heights of the tides for
the selected date, as found on the Tide Calendar.
3.
In the “Tidal Differences” column, enter the corresponding figures from the
Tidal Differences Table. Be sure to indicate + or –.
4.
Sum the figures (either add #1 and #2, or subtract #2 from #1. Watch the +
and – signs!) in the “Hampton Roads” and “Tidal Difference” columns to
complete the “Corrected Tides” column.
Date:
Location:
Name:
#1
#2
#3
Hampton Roads Tidal Difference Corrected Tides
Time of first high tide
Height (ft.) of first high
tide above mean low water
Time of first low tide
Height (ft.) of first low
tide below mean low water
Time of second high tide
Height (ft.) of second high
tide above mean low water
Time of second low tide
Height (ft.) of second low
tide below mean low water
Our Famous Tides
We have included 3 examples of high/low tide images taken at the exact same location in order to
present some perspective for people who have never experienced the tides of the Bay of Fundy
first hand.
Example 1
High Tide
Low Tide
Example 2
High Tide
Low Tide
Example 3
High Tide
Low Tide
Anchorage Alaska boasts the world's second highest tides: varying over 40 feet, low to
high tide! Bore tide (one of the three highest in the world, and a weird phenomenon:
capillary action on a gigantic scale!) occurs 2 hours 15 minutes after low tide; best
viewed between Mileposts 101 and 90 Seward Highway (26 to 37 miles from
Anchorage).
What is a tidal bore?
A tidal bore (bore = crest or wave) is a natural phenomenon which is seen in a very few parts of
the world. The Bay of Fundy is particularly noted for its extremely high tides, the highest in the
world, and for its tidal bores.
A tidal bore near Chignecto Bay, New Brunswick
A tidal bore is a wall of water that moves up certain low-lying rivers
due to an incoming tide. Tidal bores form when an incoming tide
rushes up a river, developing a steep forward slope due to resistance
to the tide's advance by the river, which is flowing in the opposite
direction. Thus we have the phenomenon of the river changing its
flow before your very eyes, flowing in OVER the outgoing river water.
The height of the tidal bore increases with the range of the tide and
may very in height from just a ripple to several feet.
Tidal bore rafting.
Some links for more info...