Kathryn Gillis

Ride down the highway with a geologist, and you will never look at roadcuts in the same way. These dynamited cliffs along roadsides expose rocks that had previously been inaccessible. Geologists studying these road cuts can decipher the processes that shaped these rocks and the surrounding landscape. Marine geologist Kathy Gillis studies the seafloor equivalent of road cuts. Faults along the seafloor at the mid-ocean ridges have ripped open the ocean crust, creating rifts in the seafloor that are as deep as six kilometers. For Kathy, the exposed ocean crust provides a window into the processes that take place under the seafloor.

Kathy in Oman - writing notes as she is mapping the geology. Oman has an ophiolite, a sequence of rocks that is thought to be similar to the oceanic crust.

The ocean crust is born at the mid-ocean ridges. There the earth’s tectonic plates spread apart and volcanic eruptions bring magma to the surface. Like a giant conveyor belt, the plates then carry the newly formed ocean crust away from the ridges until it is subducted beneath another plate. During this 100 million-year journey, the crust undergoes many changes. One of the chief culprits is seawater that circulates beneath the seafloor. This water triggers chemical reactions and deposits and removes chemicals and minerals from the crust.

The greatest changes to the crust take place in the beginning of the journey at the mid-ocean ridges. Magma heats up the water that has seeped down into the crust to as high as 750°C. The extreme heat triggers many chemical reactions. Metals and other elements leach from the crust. The scalding seawater then rises back up through the crust and spews forth from the seafloor at hydrothermal vents, carrying with it the metals leached from the crust. These metals form ore deposits on the surface of seafloor.

Kathy is particularly interested in the paths that the water takes beneath the seafloor and how it interacts with the crust. She is finding the answers in the outcrops and rifts on the seafloor.

Unfortunately, these outcrops and rifts are much harder to get to than road cuts. Kathy has dived in research submarines such as Alvin to observe and photograph these bluffs and to collect samples. She has examined cores from the Ocean Drilling Program. She also studies formations of ocean crust that are now on land. Although these structures, called ophiolites, differ somewhat from typical ocean crust, it is possible to visit them again and again.

Back in the lab, Kathy dissects the rock samples. Based on the minerals that have formed and the presence or absence of certain metals, she can determine the amount of seawater that was within the crust and the temperature of that water. She also examines tiny capsules of fluid trapped in the minerals to see how these fluids changed as they reacted with the crust.

Photomicrograph of a thin section of a rock from the lower part of the oceanic crust.

On a recent research cruise, Kathy dove on the walls of the Hess Deep; a rift that is five kilometers deep. There she observed half-a-million years of history. There were solidified magma chambers, sheeted dikes, which are the feeders that bring magma to the seafloor, ancient conduits where hot fluids flowed, and crust that was between half-a-million and a million years old. Some of the preliminary results were surprising. It had long been assumed that most of the reactions between water and crust took place deep in the ocean crust close to the magma chambers. However, Kathy and her colleagues have found evidence that sheets of lava (dikes) moving up towards the seafloor may have heated the water enough to trigger many of these reactions close to the surface. In fact, Kathy is working on a hypothesis that water may even enter the hot magma chamber. If true, her next challenge would be to figure out how this affects the formation of ore deposits on the seafloor.

Kathryn Gillis

  • Associate Professor, Earth and Ocean Sciences
  • University of Victoria

More about Kathryn

More Remarkable Careers

Melanie Holland

Melanie Holland studies the microbes that thrive in scalding temperatures surrounding hydrothermal vents. These amazing organisms not only reveal important information about the vent communities, they may also provide insights into the origin of life on Earth and the possible existence of life on other planets.

View full profile …

Dawn Wright
  • Dawn Wright
  • Associate Scientist, Geography/Marine Geology

Master Lego-constructor and former bicycle-racer Dawn Wright has immersed herself in two disciplines. As a geologist, she is studying the cracks that form in the seafloor along the mid-ocean ridge. As a geographer, she is developing software that oceanographers are using to interpret seafloor data.

View full profile …

Lauren Mullineaux

Lauren Mullineaux’s research group studies a side of benthic organisms (animals that live on the seafloor) that until recently has received little attention.

View full profile …

Jo Griffith
  • Jo Griffith
  • Principal Illustrator, Scientific and Oceanographic Data

Technical illustrator Jo Griffith hasn’t picked up a pen in over five years. Instead she uses a variety of computer programs to create graphs, maps, and illustrations for researchers.

View full profile …

Emily Klein

Emily collects rocks from the deep seafloor. The chemicals that make up the rocks provide clues to how the oceanic crust is built.

View full profile …

Wen-lu Zhu
  • Wen-lu Zhu
  • Associate Scientist, Geology and Geophysics

Wen-lu Zhu studies the properties of rocks found deep in the ocean crust by recreating those conditions in the laboratory.

View full profile …

Ashanti Pyrtle

Ashanti Pyrtle studies the fate of radioactive material that enters rivers, lakes, and oceans. She also advises minority science students on how to navigate through graduate school and prepare for a career afterwards.

View full profile …

Debby Ramsey

As Third Engineer onboard the Research Vessel Thomas G. Thompson, Debby Ramsey helps keep all of the equipment that has moving parts running smoothly.

View full profile …

Maya Tolstoy

Marine seismologist Maya Tolstoy helps find active volcanoes on the seafloor by listening for their eruptions.

View full profile …

Rose Dufour
  • Rose Dufour
  • Ship Scheduler and Clearance Officer, Ship Operations and Marine Technical Support

Rose Dufour and her job-share partner Elizabeth Brenner create the schedules for four research ships. The challenge is to keep the scientists, funding agencies, and foreign governments happy.

View full profile …

Claudia Benitez-Nelson

Claudia Benitez-Nelson uses radioactive isotopes to study the complex world of nutrient cycling in the oceans.

View full profile …

Kathryn Kelly

Kathryn Kelly studies how changing ocean currents affect the climate. And she does all of her research from the comfort of her office.

View full profile …

Amy Bower
  • Amy Bower
  • Associate Scientist, Physical Oceanography

Amy studies the interactions between ocean currents and climate. These interactions are very complex.

View full profile …

Margaret Leinen

As a scientist, Margaret Leinen studied sediments that have accumulated on the ocean floor. Now as the Assistant Director of Geosciences at the National Science Foundation, she oversees programs in Earth, Atmosphere, Ocean, and Environmental Sciences. She is also working on initiatives to bring more women and minorities into these fields.

View full profile …