It’s been said that the underwater world is the earth’s last great unexplored region.
And though the interior of Africa, the Amazon Jungle and the poles are inaccessible to all but the most fearless adventurers, they’re a far cry from the underwater wonders like the 7-mile-deep Mariana Trench, where the pressure is capable of crushing both man and machine.
Though they are and probably always will be at least partially shrouded in mystery, much is known about some of the world’s most impressive aquatic environments, like the ones we’re about to dive into.
1. GREAT BARRIER REEF, AUSTRALIA
It may come as no surprise that the Great Barrier Reef is the world’s largest and most intricate reef complex.
But what’s not so well-known is that it’s actually made up of nearly 3,000 individual reefs, more than 700 continental and mangrove islands, and approximately 300 cays.
It’s located in the Pacific along Australia’s northeast coast, and core samples indicate that it began forming on the continental shelf at least 5 million years ago.
From stem to stern it’s more than 1,200 miles (1,800 km) long, or about the length of America’s West Coast between Canada and Mexico.
It’s generally between 37 (60 km) and 155 miles wide (250 km), and in some areas as close as 10 miles (16 km) to shore, while at others more than 100 miles (160 km) out in the ocean.
And with a total area of about 135,000 square miles (350,000 square km), it’s 10% larger than New Mexico.
Though the reef has an average depth of just 115 feet (35 m) and is often even shallower close to shore, according to the Great Barrier Reef Marine Park Authority, on the outer edges near the continental slope it extends down more than 6,500 feet (2,000 m).
Exploration of the reef by Europeans began in 1770 when English explorer Captain James Cook’s ship got stuck on it.
But though the work of mapping it’s myriad passages and channels continued well into the 20th century, much is still relatively unexplored.
Like all reefs, the structure’s building blocks were formed as living polyps and hydrocorals took root on the calcified remains of those that’d lived there before, after which they became bound in place by cement-like substances comprised of algae and bryozoans – microscopic invertebrates that live in colonies.
Further strengthening the reef’s endless nooks and crannies are immense quantities of sand and skeletal waste pulverized into granules by currents and waves.
The reef has grown on the relatively shallow coastal shelf that rings much of the continent, and its nutrient-dense waters have allowed it to flourish, thanks largely to warm temperatures that generally range from 73 degrees Fahrenheit (23 C) to 29 degrees Fahrenheit (84 C) year-round.
The Great Barrier Reef is home to an astonishing array of marine species including more than 500 hard and soft corals, 3,000 types of mollusks, more than two dozen kinds of marine mammals like whales and dolphins, and about 1,500 species of fish, of which more than 100 are sharks and rays.
But though most have evolved over millennia, some like saltwater crocodiles and great white sharks have changed little since prehistoric times.
2. Galapagos Islands, Republic of Ecuador
Located about 600 miles off Ecuador’s west coast, the Galapagos Islands consist of more than a dozen islands spread over about 17,000 square miles in the Pacific Ocean.
The islands are most famous as the location where Charles Darwin spent years in the early 1800s studying local flora and fauna, an endeavor that would eventually lead to his groundbreaking theory of evolution as put for in his book The Origin of Species.
In many respects it was the perfect location, primarily because of the islands’ remoteness and the fact that they’re home to a number of isolated populations of plant and animal species that have evolved free from outside influences.
Some estimates suggest that the islands and ocean around them are home to more than 3,000 species of plants and animals, and that nearly 25% of them aren’t found anywhere else in the world.
The islands’ most notable species include a colony of penguins that are the only ones of their kind in the Northern Hemisphere, sea lions, marine iguanas, whales, sharks and Galapagos turtles – some of the oldest living animals on the planet often topping the 100-year mark.
But compared to other underwater marvels on the list, the islands are relative newcomers, and geologists think that the largest – Isabela and Fernandina – are probably less than a million years old, whereas the eastern islands of San Cristóbal and Española are probably three or four times older.
And some of the westernmost islands which are the most active volcanically may only be a few hundred thousand years old, and are therefore growing and changing much more quickly than their more aged counterparts.
The island’s formation began slowly on the sea floor, but the seamounts that now form their bases grew larger over time as extruded lava solidified and tectonic plates collided, fractured and rose.
Though the conical visible portions of the thirteen major volcanic islands in the Galapagos archipelago are impressive in their own right, they’re just the tips of submerged volcanic platforms, and some of them are much larger below the waterline than they are above it.
In addition to being a global hotspot for biologists, the Galapagos Islands are popular destinations for geologists, oceanographers, and volcanologists from all over the world.
Now nearly 97% of the islands are designated as national park, but due to their remoteness and the high cost of travel and tours, they’re visited by less than 100,000 tourists each year.
Just a few years ago an international team of scientists led by America’s Woods Hole Oceanographic Institution mapped previously unstudied sections of the ocean’s floor using high-resolution technology which revealed nearly three dozen undersea mountains forming, that will likely become new islands hundreds of thousands or millions of years in the future.
3. Lake Baikal, Russia
Located in southern Siberia near Russia’s border with Mongolia, crescent-shaped Lake Baikal claims a number of impressive distinctions.
Formed about 25 million years ago it’s not only the world’s oldest lake, but the deepest and largest by volume as well.
In fact, at 5,500 cubic miles (23,000 cubic km), Baikal contains about the same amount of water as all of North America’s Great Lakes combined – or about 20% of all the world’s fresh water.
Baikal was created from the continual fracturing of the earth’s crust, tectonic shifts, and incessant earthquakes of which even now there are often more than 2,000 a year.
These forces are still making the lake larger and deeper, and though the region’s climate is particularly harsh, the area immediately around Lake Baikal is generally more temperate due to the immense body of water’s moderating effect.
With an average depth of more than 2,400 feet (740 m), at its deepest point the lake plunges more than a mile down, and its surface area of 12,200 square miles (31,700 m) is only slightly smaller than Belgium.
The lake is nearly 400 miles (640 km) long, 49 miles (79 km) across at its widest point, and at about 1,300 miles (2,100 km) its coastline is longer than the distance between New York and Miami.
Baikal is dotted with more than two dozen uninhabited islands, but on the largest Olkhon, there’s a thriving village of about 1,500 residents.
Though more than 300 rivers and streams feed the lake, the Selenga River is its largest source, contributing nearly 50 percent of its water.
On the northern side of the lake, the Angara River is its only outlet, carrying nearly 16 trillion gallons of water northward annually that end up in the Yenisey River and eventually the Arctic Ocean.
Among the world’s other super-deep lakes, Baikal has the most oxygenated water, and its visibility often exceeds 150 feet, especially in the summer when it’s brimming with Siberian snow melt.
Baikal plays a prominent role in Russian myth and folklore and is often referred to as the “Sacred Sea,” but despite its relatively harsh climate, the lake and nearby watershed are home to thousands of unique species of plants and animals, many of which aren’t found anywhere else.
Located in the remote western Pacific between Papua New Guinea to the south and Guam and The Philippines to the east and west respectively, the Palau archipelago is one of the world’s most pristine underwater marvels.
Palau was first discovered by Europeans in the late 18th century, and over the years was claimed as territory by a number of colonial powers including Britain, Spain, Germany and Japan.
Comprising nearly 350 islands, it’s ranked as one of the 7 Wonders of the Underwater World for good reason.
It’s home to one of the planet’s oldest and most diverse coral reefs, and though it’s not the biggest, evidence suggests that it’s been in existence for nearly 2 million years, and that it’s among the most biologically diverse environments in the world.
The reef is home to approximately 700 species of coral, as well as 1,500+ different types of fish, many of which are easily seen in water that often boasts visibility exceeding 200 feet (60 m).
Palau’s unparalleled diversity is largely the result of the convergence of three major ocean currents that bring with them a continual supply of nutrient-rich water, of which phyto and zooplankton form the base of the food chain.
Characterized by shallow reefs, deep abysses, and abundant shipwrecks, it’s also home to a number of sheer drop offs like Peleliu Wall, which plunges from nearly the surface to 900 feet (273 m) down into the surrounding depths.
Sea turtles, dolphins, whales and invertebrates like anemones, starfish, octopus and cuttlefish are common, and there’s a small but thriving population of Dugong – marine mammals similar to manatees that inhabit coastal areas, dine on seagrass, and can grow up to 9 feet long (2.7 m) and weigh nearly 1,000 pounds (453 kg).
Palau is also famous for its many marine lakes, the most notable of which is Jellyfish Lake, so named because its amorphous inhabitants have evolved and flourished over millions of years in the lake’s predator-free environment, during which time they’ve lost the trademark sting for which many of their open ocean cousins are well-known.
In addition Palau’s waters support one of the densest populations of various shark species on the planet, and in 2009 the country set aside an area nearly the size of Texas – about 230,000 square miles (600,000 square km) – as the world’s first protected shark sanctuary in which fishing is banned.
5. Deep-Sea Vents
Deep-sea hydrothermal vents are like hot springs and geysers, but instead of residing on the earth’s surface they’re scattered far and wide along ocean floors worldwide.
They’re typically found in areas where two or more tectonic plates meet, but are also common where the earth’s submerged crust is porous, fractured or particularly thin.
When it circulates under the earth’s crust, cool sea water is heated by magma to temperatures often exceeding 750 degrees Fahrenheit (400 C) which causes it to expand and rise through existing fissures, dissolve mineral-rich deposits creating its own means of escape, or burst through weak and brittle areas.
The most dramatic deep sea vents are referred to as “black smokers” because their superheated coal-colored plumes eject tons of sulfur and particulate laden slurry into the ocean every second.
Black smokers often feature mineral deposit chimneys nearly 200 feet high, and their emissions can form columns that are equally as tall.
Though much of the particulate is carried away by currents, some falls back down to the sea floor solidifying into new deposits, many of which have dramatic and otherworldly forms.
Deep-sea vents are classified based on their temperatures, flow volumes, the depth at which they’re found, and the chemical composition of their ejections.
“White smokers” are generally cooler, have smaller chimneys, and emit chalky plumes that are composed of high concentrations of calcium and silicon, but under the right conditions they can be equally as impressive as their dark counterparts.
Even cooler, weaker and clearer vents are called seeps, which typically shimmer like wavy transparent mirages due to the presence of gases like carbon dioxide instead of particulate.
Though there are only slightly more than 500 known active hydrothermal vents, oceanographers agree that there are probably hundreds or thousands more that haven’t yet been discovered.
Many known vents have been visually observed, while other deeper and more remote ones are only known to exist due to recent seafloor mapping and from water temperature and chemical composition data gathered by sensors and unmanned underwater vehicles.
Before exploration became feasible, it was thought that the conditions around vents were too harsh to sustain life, but particularly around vents in the Pacific Ocean and Caribbean Sea, scientists have discovered a stunning variety of organisms that have adapted to toxic high-heat conditions that would kill other plants and animals instantly.
The conversion of mineral-rich hydrothermal fluid into energy – called chemosynthesis – that makes life possible here is a truly unique aspect of these ecosystems that doesn’t require sunlight.
Located in the Cayman Trough between Jamaica and the Cayman Islands, the Ashadze hydrothermal field was the deepest known deep-sea vent field until 2010, when another nearby plume was discovered nearly 16,000 feet (5,000 m) down.