Oceans have lakes and rivers.
The Earth’s oceans are just as dynamic a landscape as the bits of rock that peek above its surface. Our seas are home to the world’s longest mountain chain, its deepest trenches, and other impressive natural structures that boggle the mind. The ocean is even home to its own underwater lakes and rivers. When seawater seeps up from the seafloor, it mixes with the salt layers above and creates a depression in the seabed, where this heavy, dense, and briny mixture rests. Some of these depressions can be more like puddles than proper lakes, stretching only a few feet across, but others can be many miles wide or long, and even feature their own underwater waves. And like lakes and rivers on land, these underwater features also have coastlines and animals that rely on these salty seas within seas to survive.
These aren’t the only types of “rivers” found in the world’s oceans. Where some of the world’s major rivers (including the Amazon and Congo) meet the sea, an underwater current of silt and sand can create massive channels that move more sediment in a few weeks than all the world’s regular rivers combined can move in a year. Although these are massive undersea structures, scientists discovered them only 40 years ago with the advent of sonar mapping, and many mysteries still surround them. In fact, some oceanographers have said that we know more about the surface of Mars than the depths of the Earth’s oceans, and less than 19% of the ocean floor has been mapped in detail. Which raises the question: What other amazing aquatic wonders have yet to be discovered?
Volcanic eruptions are some of the most dramatic geologic events that humans can witness, but a large majority of them actually happen without us noticing. The National Oceanic and Atmospheric Administration (NOAA) estimates that 80% of all volcanic eruptions occur underwater — but these explosive Earth burps don’t work the same way as their land-based relatives. Because the weight of the water above these volcanoes creates such high pressure, submarine volcanoes rarely truly explode. Instead they create what’s called “passive lava flows” along the seafloor, which over the course of millions of years can form volcanic island chains such as Hawaii. These submarine volcanoes that never peak above sea level are known as seamounts, and their lava-churning drama occurs out of sight and (for most of us) out of mind.
