“She eyes me like a pisces when I am weak
I’ve been locked inside your Heart Shaped box for weeks
I’ve been drawn into your magnet tar pit trap
I wish I could eat your cancer when you turn black” –Nirvana, Heart-Shaped Box
By looking at the right combinations of wavelengths of light, one can literally find almost anything in the depths of space.
But back on Earth, we have some surprising natural features that have been captured from above with nothing more than a camera.
The International Space Station completes an orbit of the entire Earth every 90 minutes or so, moving along at a clip of around 25,000 kilometers an hour. Because of the capabilities of the cameras on board, it can find never-before-seen areas of both the continents and the oceans.
And I bet you’ve never seen a photo of Earth like this one.
You might be wondering to yourself just how on Earth something like this came to be. It’s not a cloud; it’s not a stunt-plane trail.
It’s known as an atoll, and they’re found interspersed throughout the oceans on Earth. Here, have another.
So where do these atolls — found almost exclusively in the Pacific and Indian Oceans — come from? Believe it or not, it all starts with a volcano, and not just anywhere, but at the bottom of the ocean!
At many different locations on the sea floor, liquid magma from deep within the Earth’s mantle rises up through the crust, emerging from below. The molten rock enters the Ocean waters — typically at about 4° Celsius — at temperature up to 1200° Celsius! And you can very easily imagine exactly what happens. On one hand, the lava emerging into the ocean immediately heats up and boils off large quantities of water, for as long as the eruption takes place!
But on the other hand, what happens to the rock? Being much denser than water, after the initial eruption, it cools and sinks down to the bottom of the ocean, flowing down to as low a point as possible. It’s this very process that’s going on off of the coast of the Canary Islands right now, at El Hierro.
Over a long enough time period of continued, successive eruptions, the cooled lava forms a conical structure, reaching closer to sea level and the atmosphere above it.
When the undersea cone is built up high enough, lava eruptions can pierce through the interface between the ocean and the atmosphere — for the first time — and when it cools, it can begin to create land. This is how, perhaps most famously, all of Hawaii was created! In fact, it’s still being created, as Hawaii’s Kilauea first surfaced above the Ocean just 23,000 years ago, and its seamount Loihi will do so just a few thousand years into the future!
Once the lava flow ceases and this volcanic cone becomes extinct, you’ll find yourself left with a relatively stable Oceanic island. From this point, two important things — one of which is unavoidable and the other which requires the right conditions — happen.
The one that requires the right conditions is that, on the sides of this mountain, beneath the surface of the water, a fringing coral reef begins to form. It can take up to 10,000 years for a fringing reef to form, but if it does, what happens next is truly amazing. Coral is one of the most slowly growing features, made up of individual organisms (polyps) that are mere milimeters in size. Over time periods on the order of 100,000 years, if conditions are right, the reef grows in size, outwards, in the shallow waters around the island.
The island itself, however, whether it successfully grows a large coral reef or not, will erode over time. A combination of wind, the ocean, and weather will, over geologically long time periods, wear the island itself away. Oftentimes, what looks like the rim of a crater will be the last piece of land to survive before the entire island is weathered away.
But while the island weathers away, if it happens to have a fringing reef that’s grown outwards around it, the coral is quite capable of growing downwards as well, to keep up with the ever-submerging island. While coral reefs thrive just a few meters beneath the surface, some coral organisms can survive down to depths of 3,000 meters, or nearly 10,000 feet! What usually winds up happening is the coastline shrinks away from the coral, which in turn continues to grow outwards into the ocean beyond. When you get a separation between the coast of an eroding shore and the coral reef that grows out into the ocean, that’s called a barrier reef!
But while it may take 100,000 years or more for a great coral reef like this to form, it may take up to — wait for it — 30 million years for the island to erode completely away!
When it does, the coral continues to grown downwards to remain anchored to the mountain beneath it, maintaining its shallow depths just barely beneath the ocean’s surface. That final stage, where a large, circular coral reef simply encloses an empty, landless lagoon, is what forms an atoll!
The culmination of over a hundred thousand years of organism growth underwater, followed by millions of years of erosion of a once-proud island, is what it takes to create these beautiful and elusive sights.
Perhaps what’s even more amazing is that this story — the accepted theory on the formation of these atolls — dates back to none other than Charles Darwin!
So remember, astronomy isn’t only amazing when we look up; sometimes there’s great joy, beauty, and science in remembering to look down, too!