Frequently Asked Questions
Every week we receive and read e-mail from fellow web surfers. We appreciate your feedback, and your sharpness in noticing our errors. We have made a list of frequently asked questions in the hope they will respond to your enquiries.
For further information, please contact the Canadian Hydrographic Service by e-mail at chsinfo@dfo-mpo.gc.ca.
For definitions of terms, please visit the glossary.
Questions:
What causes the tides?
For further information, please visit the Tides and Currents information page.
Why tides are important to humans?
Are there Tides in the Great Lakes?
For further information, please visit the Great Lakes information page.
What is a seiche and when does it occur?
A seiche is a standing wave that occurs in an enclosed or semi-enclosed water body and is usually caused by strong winds and/or changes in atmospheric pressure. The seiche can continue, in a pendulum fashion, even after the cessation of the originating force.
In Canada, strong seiche action can be observed on Lakes Erie and Ontario, in Sydney Harbour (N.S.), in the Bay of Fundy and Gulf of Maine.
For further information, please visit the Seiches information page.
What are Tidal Bores?
A tidal bore is the leading edge of the rising tide as it enters a river. It is a wave like phenomenon that moves up the mouth of rivers which are subjected to exaggerated tides.
Exaggerated tides in Canada can be seen in the Bay of Fundy on the East coast of Canada. The largest bore in the Bay of Fundy occurs on the Petitcodiac River. The bore or wall of water travels upriver at about 8 mph and is about 1 meter (3 feet) high during spring tides when the Moon is full or new. Tidal bores are most pronounced where river channels narrow.
For further information, please visit the Tidal Bores information page.
What are "Reversing Falls"?
For further information, please visit the Reversing Falls information page.
What is a Tide Rip?
For further information, please visit the Tide Rip information page.
What is a Rip Tide?
What are Spring and Neap tides?
The height of the tide varies from day to day but the fluctuations are predictable. They are mainly caused by: 1) the degree to which the sun and moon's influences are acting in the same direction; and 2) the varying distance between the moon and the earth.
Twice each month, at the time of the new moon and the full moon, the gravitational influences of the moon and sun reinforce one another and cause the tides to rise to greater heights and fall lower than average tides. These are called spring tides from the Old English word "springan" which means to well up. At the time of the quarter moon, when the sun, earth, and moon form a right angle, the difference between high and low tide is less than average. These are neap tides, from the Old English "nep", as in nipped in the bud. Every 27 and a half days, when the moon reaches a point in its orbit closest to the earth (called perigee) the tidal range is increased. When perigean tides coincide with spring tides, extreme tides can be expected. Example, in the Bay of Fundy, these conditions may create tides as large as 16 meters (53 feet). Conversely, when the moon is at apogee, its farthest point from the earth, even spring tides are diminished.
What is a tsunami?
Japanese word that means "harbour wave". Tsunamis are huge ocean waves caused by an undersea disturbance generating a vertical motion to the water column. These disturbances are triggered by volcanoes that erupt under water or by earthquakes and landslides that occur underwater.
The waves of the tsunami spread in a circular manner from the point of disturbance and can move large distances without a great loss of energy. Their speed can reach more than 800 kilometers per hour. In deep waters, tsunamis are less than a meter high. However, when they reach shallow waters or narrow bays, the waves slow down and pile up into a tall wall of water which causes devastation to things on shore. The first wave of a tsunami is often preceded by a lowering of the water level. When the tsunami hits the coast, it appears like a rapid rise in water level instead of a breaking wave. Earthquakes outside Canada have caused tsunamis which have damaged the Canadian coastline.
For further information, please visit the Tsunamis information page.
Where are the largest tides in the world? What causes them to occur there?
Where can I obtain Canadian Tidal predictions?
There are 7 separate volumes of the Canadian tide and current tables:
- Volume 1 covers the Atlantic Coast and the Bay of Fundy;
- Volume 2 covers the Gulf of St. Lawrence;
- Volume 3 covers the St Lawrence and Saguenay Rivers;
- Volume 4 covers the Arctic and Hudson Bay;
- Volume 5 covers Juan de Fuca Strait and the Strait of Georgia;
- Volume 6 covers Discovery Passage and the West Coast of Vancouver Island;
- Volume 7 covers Queen Charlotte Sound to Dixon Entrance.
You can purchase the Canadian Tide and Current tables, which provide one full year of predictions from over 800 authorized chart dealers across the country and internationally.
By calling 1-877-775-0790, you can find out vocal tidal prediction.