Yorkshire Philosophical Society

Event Information

Exploring Hades: geomorphology and sediments of the deepest places on Earth

Dr Heather Stewart, British Geological Survey, Edinburgh

The deepest parts of the ocean are one of the final remaining frontiers of discovery on our planet. Much of the deep ocean is unmapped and draws in explorers, scientists, cartographers and environmentalists, keen to discover its secrets. Heather Stewart from the British Geological Survey has been lucky enough to participate on a number of expeditions to explore the deepest sea-floors and will share some of what these diverse expedition teams have learned.

Lecture to be held in the Tempest Anderson Lecture Theatre, Yorkshire Museum,
YO1 7DR at 7pm

ALL WELCOME.

Image: Sirena Deep, Five Seas Expedition by Atlantic Productions for Discovery Channel, 2020.

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Member’s Report

Heather Stewart was the geologist on the Five Deeps Project, funded by Victor Vescovo of the United States. Having climbed the highest peaks on each continent and skied to both North and South Poles, he aimed to visit the deepest point in each of the five Oceans. See: https://fivedeeps.com/

Dr Stewart’s research areas include studying the geomorphology and sediments of hadal ecosystems found in deep subduction oceanic trenches (below 6000 metres).  Her lively talk to the YPS that evening gave us the chance to accompany the dives and feel the excitement of the discoveries of marine life and physical character of the sea bed at depth.

She gave an outline of the research of Heezen and Tharp from 1952 onwards which led to the identification of the mid-Atlantic Ridge and then to Plate Tectonics: the theory of the Earth’s surface being comprised of large plates of oceanic and continental crust that move slowly over the Earth’s rocky inner layer, explaining many phenomena, including mountain building events, volcanoes, and earthquakes.

Some areas of sea floor are mapped from acoustic surveys from the surface, but most is only known from satellite surveys that estimate depth from small differences in surface height. The Five Deeps Expedition allowed the exploration of the features and character of deep trenches and included a major multi-disciplinary scientific programme led by Dr Alan Jamieson of Newcastle University providing the opportunity to sample life across a gradient of depths, temperatures, salinity, food supply, latitude and in places around the world that were formed, split, or united millions of years ago by the shifting of the Earth’s tectonic plates.

DSSV Pressure Drop carried the crew and equipment on the expedition. DSV Limiting Factor was the manned submersible capable of descending with up to two people to depths of 11 kilometres, surviving pressures of 1100 atmospheres and with the life support to bring them back up after many hours. There were also three unmanned ultra deep sea remote robotic landers, able to send images to the other vessels, collect samples and probe the sediments on the sea floor. It had taken three years for engineers, oceanographers and scientists to plan the expedition and design and test the Limiting Factor submersible, built by Triton Submarines, LLC.

From October 2018 to August 2019, a number of different features and depths were explored to discover their ecosystems and organisms. New species were identified and known species discovered much deeper than expected. The inhabitants have adapted and evolved in order to withstand the extreme environment in which they live; intense pressures of the Hadal Zone, the near-freezing temperatures at great depth, low food supplies, perpetual darkness and frequent seismic disturbance. The five deeps were the Puerto Rico Trench in the Atlantic, South Sandwich Trench in the Southern Ocean, Java Trench in the Indian Ocean, Challenger Deep in the Pacific and Molloy Deep in the Arctic. All the trenches were carefully surveyed and measured and were between 5500 metres and 10925 metres below sea level.

Heather Stewart described the geological significance of the images of sea mounts, 500 metre cliffs and submarine landslips; the trenches are the result of continuing tectonic activity, where earthquakes cause massive earth movements and tsunamis, such as the Boxing Day Tsunami of 2004. Many older slides were identified and dated. She also described the exhilaration and exhaustion of her dive in the sub in the Arctic Ocean down to 2500 metres over long hours and in confined space as like a moon command module.

Paul Thornley

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