Storm surges occur in coastal areas when strong onshore winds and low atmospheric pressure during passing storms raise water levels along the shore above predicted levels. Storm surges occur on all four Canadian coasts (Pacific, Arctic, Atlantic and Great Lakes). The most severe known surges in Canada have been 2 to 3 metres high (well over the head of the average person). Severe storm surges that occur on high tides or during high lake levels can result in flood damage, evacuation of communities and loss of life. This map shows that a qualitative estimate of storm-surge hazards for selected representative locations varies in severity and frequency in different areas of coastal Canada. On this map, a low frequency means one surge every few years, a medium frequency indicates one surge every year and a high frequency represents several surges every year. Low severity corresponds to some flooding or erosion during large surges, with minor resulting damage. Medium severity indicates moderate flooding or erosion during large surges, with moderate damage. High severity means extensive flooding or severe erosion during large surges, with significant damage.