We know more about the surface of the moon or Mars than we know about the surface of the Earth! This is because over 70% of Earth is hidden under water that easily absorbs electromagnetic waves. While satellites and telescopes can look far into the universe, these tools cannot see to the bottom of our oceans.
Therefore, we rely on sophisticated geophysical techniques to ‘see’ the seafloor. These so-called ‘remote sensing’ methods use electric and magnetic fields, variations in gravity, or sound waves (similar to echo-sounding techniques used by bats) to image the topography of the seafloor.
Resolution vs. coverage
Satellites provide a global overview of the seafloor topography, but only in a resolution that reveals large mountain chains, deep trenches, and huge, isolated volcanoes. Ship-based measurements still have to ‘look through’ on average 4000 m of water, but achieve a resolution of around 50 m (i.e., the smallest object we can detect must have at least the dimensions of a football stadium). Such measurements are limited in their extent, as a ship physically has to sail over the area. Therefore, less than 10 % of the seafloor has been mapped at this resolution. We can increase the resolution further by using robots to ‘fly’ close to the seafloor (link), so we are able to see features of about a few meters in extent (i.e., an object with the dimensions of a football goal would be clearly visible). This information is of high value, as it shows us the geological diversity of the seafloor with an incredible amount of detail; However, the area we can cover using robots is even more restricted, so a total of less than 1 % of the seafloor has been mapped at this resolution.
What is down there?
Satellites, ships, robots – why do we invest all of this effort just to map a flat, featureless plain of sediment? Actually, the seafloor shows a great variety of geological features, including: volcanoes, lava flows, hills and valleys, mountain chains, large cracks and deep fissures. We map the seafloor to give us information about global plate tectonics, volcanic processes, hydrothermal venting, and habitats of deep sea fauna. To study these things, we analyze the various shapes of seafloor features, and combine them with information we obtained during sampling and direct visual observations (e.g. from robots or manned submersibles). Together, these things combine to generate a ‘geological map’ of the seafloor.
Mapping activities of the Marine Mineral Resources group
The MMR group is dedicated to understand the relationships between tectonics, volcanism, formation of hydrothermal vents, and related metal deposits in various settings on the seafloor. Geological mapping of the seafloor is a key tool to combine the broad range of geological disciplines, ranging from deep-sea geophysical surveys to laboratory geochemical analyses.
With so much of the Earth left to explore, and new discoveries being made during every expedition, this is truly one of the last frontiers on Earth.
All maps shown are from the following publication: