The deep ocean floor was once thought to be flat and barren. This idea was quickly put to rest with the first efforts to reveal that which exits in perpetual
darkness. Those first efforts, which consisted of lowering weights until they hit bottom (called soundings), demonstrated the ocean floor was anything
Mapping features of the ocean floor by lowering weighted lines however, would be a daunting task. Perhaps it is a good thing those first measures were more intended for identifying navigable routes then identifying the shape of the ocean floor.
With the Challenger expedition in the late 1800s, things began to change. This expedition provided the first outline of the ocean floors and sparked more interest in exploring the deep. It also found the deepest known location in the ocean at the time within the Mariana Trench at a depth of 8,184 metres.
In the 1900s, war played a role in advancing our knowledge of the ocean floors. This was driven by the development of submarines, which required a method of navigating the depths – SONAR. Data collected from SONAR during World War II provided the basis for the development of the first real maps of the floor of the north Atlantic by Bruce Heezen and Marie Tharp in 1957.
These maps played a critical role in the birth of plate tectonic theory and the deep sea exploration that came with it.
But the most amazing discoveries in the oceans were still to come.
A significant part of the Heezen and Tharp work is the mapping of the Mid Atlantic Ridge and its rift valley. The Mid Atlantic Ridge is a staggering 16,000 km long, and it is volcanically active. Its rift valley, which runs along its spine, identified this mountain range as being where the ocean floor is spreading. The rift itself is massive. It is the depth of the Grand Canyon, but with a width of 80 to 120 km (compared to 6 to 29 km).
While the Mid Atlantic Ridge is a long mountain range, it is a part of a much larger range. Called the Mid Oceanic Ridge, this mountain range is nearly 60,000 km long and wraps around the planet like the seams on a baseball.
The Mid Oceanic Ridge spans the globe. (Source :J M Watson / USGS via Wikicommons)
Not only is the ocean mountainous, it is home to both the tallest mountain on Earth and the mountain with the largest base on Earth. The tallest might be easy to guess. It is Mauna Kea – one of the Hawaiian Islands. While it has an altitude of only 4,205 metres, if measured from its base, it is over 10,000 metres tall (Mt Everest is 8,850 metres tall). The mountain with the largest footprint however? Well, technically speaking, it is a volcano, but Tamu Massif (which was only identified in 2013), is not just the biggest volcano on Earth, but also one of the largest in our solar system. While it is not tall, its footprint covers close to 26,000 square kilometres – about the size of the British Isles.
Gigantic trenches - check. Gigantic mountain ranges – check. Gigantic volcanoes – check.
The ocean is also home to the largest cliffs on our planet. In the Bahamas, there are undersea cliffs with sheer drops of up to 4000 metres.
It is also home to vent systems, of which some have grown to gigantic proportions.
Left: Black plumes of superheated (350 degrees Celsius) hydrothermal fluid billows from a black smoker. (Source: NOAA via Wikicommons)
Right: An active vent on the top of Poseiden emits a 50 degree Celsius hydrothermal fluid. (Source: NOAA Photo Library via Wikicommons)
One example is Poseiden, a vent chimney which is a part of the Lost City vent system, located in the mid Atlantic Ocean. Poseiden towers 60 metres above the sea floor, making it the tallest of the tall – the chimneys of the Lost City are the largest known vent structures in the ocean.
While black smokers and the chimneys of the Lost City are both hydrothermal vent systems, they are quite different. Where black smokers emit sulphur-rich compounds which give them a unique appearance of black smoke billowing from them, the Lost City is a system of white smokers. These vents emit a whitish appearing fluid comprised of carbonates, and as a result take on a ghostly white appearance. The chimneys of the Lost City are composed primarily of limestone. The most common minerals found in the chimneys are aragonite, calcite, and brucite.
A close-up of terrestrially formed aragonite, from our giftshop, the Company Store.
While the sizes, ages, and formation rates of all of these giants differ, there is one thing that they hold in common – volcanism. It is estimated that 90% of the world’s volcanic activity occurs on the ocean floor. This land beneath the surface is perhaps the most dramatic, dynamic, and diverse on our planet, and we have only explored a small portion of it.
Imagine what other giants await our discovery.
Header Photo: IFE, URI-IAO, UW, Lost City Science Party; NOAA/OAR/OER; The Lost City 2005 Expedition. / NOAA Photo Library / Wikicommons