Explore The Ocean Floor
Oceans cover approximately 72% of Earth’s surface and contain 97% of Earth’s water. The oceans play an important role in climate regulation, weather patterns, the carbon cycle, and the water cycle. They provide valuable resources to people and are a habitat to more than 230,000 species (that we know of!)
Much like the water in the oceans, light from the sun is a crucial part of marine life. The ocean is divided into layers, or zones, from the top to the bottom. Each zone is determined by how much light it receives. The sunlit and the twilight zones receive the most light, while the ocean floor and ocean trenches are usually completely dark. Today we will be using Google Maps satellite view to investigate the features of the ocean floor. Read about each feature and then explore the locations provided in Google Maps.
Shallow Bays and Estuaries
The Chesapeake Bay is an inland estuary in North America. Its watershed covers 6 states, and its mouth is connected to the Atlantic Ocean. The bay is a complex ecosystem providing a habitat and spawning ground for millions of organisms. The bay is shallow- its average depth is only 21 feet. This allows grasses and animals such as crabs and clams to cover the bay floor.
Notice the man-made channel in link #2. Why do you think this was dug out of the bay floor?
Continental Shelf
Starting at a continent’s shoreline and extending into the ocean is the continental shelf. This ocean floor feature is relatively shallow with an average depth of 400 feet and can stretch out from land anywhere from 45 – 900 miles. Most marine organisms live on the shelf or in the waters above it.
Great Barrier Reef Continental Shelf
Look at the continental shelf on the east coast of the United States. Where is the shelf the narrowest? Where is it the widest?
The Great Barrier Reef link shows a section of the reef at the edge of the continental shelf. What signs of life do you see?
Continental Slope
Imagine walking underwater straight across the continental shelf. Eventually, you would come to the end of the shelf and the ocean floor would start descending steeply towards the very bottom of the ocean. This steep descent is called the continental slope and can have a pitch anywhere between 4 and 90 degrees. Areas of the continental slope are bisected by submarine canyons. These canyons were formed by erosion when water drained into ancient seas. The link below shows the mouth of the Chesapeake Bay, the continental shelf, and a canyon just east of Virginia Beach called the Norfolk Canyon.
North American Continental Slope
Travel north along the continental slope and you will see the Washington Canyon, Baltimore Canyon, and the Hudson Canyon, the largest on the East Coast. What US state is the Hudson Canyon adjacent to?
The Gulf of Guinea has off the coast of Africa shows both a steep and gentle continental slope.
Continental Rise
At the bottom of the continental slope one will find the continental rise, an underwater hill composed of tons of sediment that has washed off the continents. The continental rise has a wide, gentle incline that is flatter than the continental slope. Scientists study the sediments that make up the continental rise to learn about the historical geology of the Earth. Beyond the continental rise stretches the abyssal plain, an extremely deep and flat area of the sea floor.
Zoom in and out to get a view of the continental rise at the bottom of the steep continental slope. Where else can you find a visible continental rise?
Abyssal Plain
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3,000 meters and 6,000 meters. They are among the flattest, smoothest, and least explored regions on Earth. Tectonic boundaries (large cracks in the Earth’s crust where tectonic plates meet) run through some areas of the abyssal plain.
The abyssal plain is mostly flat, however, there are some features scattered throughout. What do you see on the Atlantic’s abyssal plain?
Mid Ocean Ridge
A mid ocean ridge is an underwater mountain range that forms along tectonic plate boundaries. Magma forces its way through a tectonic boundary, and new ocean floor is formed. This type of plate boundary is responsible for sea floor spreading – a process in which tectonic plates “grow” and push away from each other. This type of plate boundary is known as a divergent boundary.
The Mid-Atlantic Ridge formed at the edges of the North American and Eurasian Plates. Follow it up and down the center of the ocean. Where does it start and end?
The Mid-Atlantic Ridge is located mostly underwater, however, one portion has enough elevation to rise above the surface of the ocean. Where is that location?
Ocean Trenches
An ocean trench is a long but narrow depression in the sea floor. They are often located along convergent plate boundaries, where two plates move towards each other and one plate is forced under the other. Challenger Deep is the deepest known point in the Earth’s oceans and is a part of the Marianas Trench. At 25,827 feet, Challenger is deeper than Mt. Everest is tall.
Look at all three examples of an ocean trench. In addition to a very deep trench, what else do all three sites have in common?
Volcanic Islands
Volcanic islands can form near a plate boundary as a result of tectonic activity. When two tectonic plates collide and one slides under the other, volcanoes on the sea floor can form. Over time those volcanoes build up, some eventually rising above the surface of the ocean. Volcanoes that form near a tectonic plate boundary often form a semi-circular shaped island chain known as a volcanic island arc.
Underwater volcanoes can also form over abnormally hot mantle locations called hot spots. Hot spots can occur at plate boundaries or in the middle of a tectonic plate. As a tectonic plate slowly drifts over a hot spot, a chain of islands is formed.
Look at the volcanic island examples below. Label each as a volcanic island arc or volcanic island hot spot.