Ever since humans first took to the seas thousands of years ago, sailors have faced numerous dangers. Ancient civilizations tried to explain these dangerous conditions by claiming that they were the work of angry gods or monsters.
While scientific explanations have been advanced for dangerous phenomena such as high waves, hurricanes, and treacherous ocean currents (steady flows of water in a prevailing direction), many lives are still lost in the water each year, mainly due to drowning or hypothermia.
Hypothermia is a condition where the core body temperature becomes too cold to function properly. Prolonged exposure to waters that may initially seem warm, between 70°-80°F (21°-27° C), can cause death from hypothermia.
Some of the earliest written works make references to the dangers of the seas. In the Odyssey, Greek poet Homer mentions a great whirlpool that a group of Greek warriors encountered on their return home from the Trojan War.
Many scholars assume that Charybdis, the whirlpool mentioned by Homer, is a whirlpool that still swirls today between mainland Italy and the island of Sicily. Viking poems refer to another famous whirlpool, the Maelstrom, which lies off the rocky coast of Norway.
Several factors, working alone or together, can create whirlpools. Ocean currents that converge (come together) can cause a whirlpool. Tides and rock formations can create a whirlpool by forcing ocean currents to flow in a circular motion, as in the Maelstrom. Also, constant winds on the ocean can create or contribute to a whirlpool, as in the narrow waters between Italy and Sicily.
Although movies and literature sometimes refer to people or ships being drawn down into a whirlpool, this rarely happens. Whirlpools can pose a moderate danger to small crafts, as they can experience turbulence or even capsize (turn over) in whirlpools. Modern navigation allows ships to avoid large ocean whirlpools.
Today, the greatest danger posed by whirlpools is on rivers, where curious boaters often wander too close to whirlpools and quickly find themselves in their midst.
Cape Horn and the Straits of Magellan
Cape Horn and the Straits of Magellan lie at the southern tip of South America where the Atlantic and Pacific Oceans meet. The Straits of Magellan are a narrow passage between mainland South America and Tierra del Fuego, a large island to the south of the mainland. Portuguese explorer Ferdinand Magellan (1480-1521) discovered the Straits of Magellan in 1520 during his trip around the world.
The Straits of Magellan are narrow and often experience rough seas due to high winds. The Atlantic and Pacific Oceans are at different levels, which cause churning currents when their waters meet in the Straits of Magellan. These powerful currents caused numerous ships to sink in the Straits of Magellan.
Isaac Le Maire (1558-1624), a Dutch merchant and explorer, discovered Cape Horn in 1615. Le Maire was looking for a different and safer route between the Atlantic and Pacific Oceans. Le Maire found a different route in what is today called Cape Horn, but it did not prove to be much safer than the Straits of Magellan.
Cape Horn has violent weather patterns as a result of the meeting of the Atlantic and Pacific Oceans. Cold air moving north from Antarctica also contributes to the foul weather. Large waves, some over 65 feet (20 meters) tall, often sank ships that tried to round Cape Horn’s rough seas.
The opening of the Panama Canal in 1914 eliminated the need for most ships to travel through the Straits of Magellan or around Cape Horn in order to pass between the Atlantic and Pacific oceans.
Hurricanes, typhoons, and cyclones
Hurricanes include circular bands of clouds that slowly swirl around a central core of low atmospheric pressure (the pressure exerted upon Earth’s surface by its atmosphere at a given point), called the eye.
A hurricane may be hundreds of miles (kilometers) across, but the eye of the storm is typically only 10-30 miles (16-48 kilometers). Winds are strongest around the eye and weaken further out from the eye. A hurricane that occurs in the Indian Ocean is called a cyclone, and those in the middle and western Pacific are called typhoons.
The low pressure of the eye pushes a wall of water in front of the storm called a storm surge. The storm surge is often the most destructive part of a hurricane. Storm surges can sink ships at sea, destroy buildings on the coast, and cause flooding inland.
Hurricanes are divided into categories based on the speed their sustained winds. A category 1 hurricane produces sustained winds of 74-95 miles per hour (119-153 kilometers pr hour) and storm surges 4-5 feet (1.2-1.5 meters) above normal tide levels, enough to flood low-lying coastal roads and buildings.
Category 2 storms contain winds 96-110 miles per hour (154-177 km per hour) and produce storm surges 6-8 feet (1.8-2.4 meters) above normal tide levels, enough to flood coastal escape routes (roads and bridges leading away from the coastline) and require some people to evacuate their beachside homes.
A category 3 hurricane has sustained winds of 111-130 miles per hour (179-209 km per hour) and storm surges 9-12 feet (2.7-3.6 meters) above tide levels. Storm surges this high can cause major erosion (wearing away) of beaches and destruction of houses and businesses on and near the beach.
A category 4 storm produces winds of 131-155 miles per hour (211-249 km per hour) and storm surges 13-17 feet (4-5.1 meters) above normal tide levels. Wave action from category 4 storms can destroy buildings constructed on land less than 2 feet above sea level, and can cause flooding up to 6 miles (10 kilometers) inland.
A category 5 hurricane has sustained winds over 155 miles per hour (249 kilometers per hour) and brings a storm surge 18 feet (5.5 meters) or more above normal tidal levels. Besides massive building damage from wave action and winds, damaging floods occur more than 10 miles (16 kilometers) inland, and large-scale evacuations of coastal communities are necessary. Only three Category 5 hurricanes have ever hit the United States as of 2004.
A storm with sustained winds between 39-74 miles per hour (63-119 kilometers per hour) is called a tropical storm. Tropical storms are known for their ability to produce large amounts of rainfall over a short time. An organized storm with sustained winds below 39 miles per hour (63 km per hour) is called a tropical depression. A tropical depression can become a tropical storm and possibly a hurricane.
Nor’easters, or Northeast winter storms, are large winter storms that dump snow and ice on the coastlines of America’s mid-Atlantic and New England states. Nor’easters have struck as far south as Florida. Nor’easters typically occur between October and April. Unlike hurricanes, which rotate, a Nor’easter is a single storm line.
A single Nor’easter may stretch for over 900 miles (1,448 kilometers). Nor’easters may pack strong winds and waves, causing beach erosion and blizzard conditions in coastal cities. Ships at sea during a Nor’easter often face waves and swells over 50 feet (15 meters) high.
Nor’easters form when warm air from the southeastern United States creates an area of low pressure just off the coast. Northeastern winds pull the warm air in the low-pressure system up the East Coast. The system picks up moisture from the Atlantic Ocean as it moves north. Cold air from Canada then mixes with this moisture-filled air. The product is a line of strong storms carrying snow and ice.
Icebergs are large chunks of ice that break off from glaciers or icepacks (a large expanse of floating ice) and float in the oceans. A glacier is a slow-moving solid pack of ice and snow that forms over thousands of years.
Most of the world’s glaciers were formed between 10,000 and 15,000 years ago during the last Ice Age. Most glaciers slowly flow toward the sea. When a large piece of a glacier pushes out into the sea, it breaks away from the glacier and becomes an iceberg.
Most icebergs break away from glaciers in Greenland or Antarctica. While the majority of icebergs remain far to the north, out of the way of most ships, every year several hundred icebergs drift into areas containing shipping routes. These icebergs pose a major risk to ships.
An iceberg can create a large hole in a ship and cause major damage or even sink the ship. The most famous example of this is the Titanic, which hit an iceberg in the north Atlantic Ocean in 1912. The ship sank within hours, killing more than 1,500 people. Following the sinking of Titanic, several nations formed the International Ice Patrol to search for icebergs and record their positions.
Modern technology is also capable of detecting icebergs in shipping lanes during the day and night, and in bad weather as well as clear skies. An instrument called synthetic aperture radar that orbits Earth aboard a satellite (vehicle that orbits Earth) collects and sends pulsed signals back to Earth, where a digital map of icebergs, their size and shape, and their precise location is formed.
Reefs and rocks
Like icebergs, reefs and rocks near the shore can damage the hull of ships, causing them to spill their cargo and even sink within a short time. A reef is an underwater ridge of rock or coral (tiny marine creatures with hard exterior skeletons) that lies just below the surface. Rocks can be difficult to spot with the eye, and it is nearly impossible to see a reef before a collision.
Many modern ships rely on sonar (images produced by sound waves) or satellite technology (images produced by light waves) to detect rocks and reefs, but accidents still occur. In 1989 oil tanker Exxon Valdez ran aground on a reef in Prince William Sound, Alaska, causing an oil spill of 11 million gallons (46.5 million liters) into the Alaskan ecosystem.
While the Exxon Valdez was not one of the largest oil spills in history, it did have a major impact on the environment and shipping regulations. The ensuing cleanup cost over $2 billion, and the Prince William Sound ecosystem continues to recover to its former level of biodiversity (range of varying plant and animal species).
Animals in the seas
Although sharks, jellyfish, and other sea animals do injure people in the ocean every year, the number of these attacks are usually sensationalized. Between 70 and 100 shark attacks on humans occur throughout all the oceans worldwide each year. On average, five to ten people die every year as a result of these attacks. Americans are over 300 times more likely to be killed by a car crash involving a deer than by a shark attack in the ocean.
Many coastal states monitor shark populations in beach areas where sharks and humans mix by regularly counting and mapping shark populations according to geographic features in their habitat. Areas can use this data to issue shark advisories to beachgoers when shark populations are observed to be greater than the normal number of sharks.
Most jellyfish stings cause pain, but they rarely kill humans. One exception is the sea wasp or box jellyfish (Chironex fleckeri) that lives in the waters off northern Australia and Southeast Asia. This species of box jellyfish carries venom (poison) in its tentacles powerful enough that a single sting can cause death without prompt medical treatment.
All jellyfish species however, are passive hunters; they do not attack prey for food, but wait until a potential food source (including humans) bump into their tentacles.