Because Earth’s land and submarine canyons look similar, researchers have traditionally surmised that they formed through similar processes. Evaluating that assumption has proven difficult, however, due largely to lack of data. “Scientists have more high-resolution imagery of the surface of Mars than of Earth’s ocean floor,” according to one recent statement.
Stephen Dobbs, a Ph.D. candidate in geological sciences at Stanford University, explained the shortage of high-resolution imagery and data for submarine canyons. While orbiting satellites can readily collect high-resolution topographic data of Mars, similar satellites can collect bathymetric data for Earth’s oceans on only about a kilometer scale of resolution. Laborious and expensive processes requiring the use of ships and autonomous underwater vehicles must often be used to image the seafloor, he added.
As detailed in a new study published in Geology, Dobbs and his collaborators used open-source multibeam sonar data, along with topographic data, to compare land and underwater canyons. The study came out of a student-run seminar directed by George Hilley, a tectonic geomorphologist, and Tim McHargue, a deepwater sedimentologist and marine geologist, both also at Stanford.
Deciphering Differences
“The qualitative resemblance between terrestrial and submarine channels has led to instinctive assumptions about the similarity of the processes that form them,” Charles Paull, a senior scientist at the Monterey Bay Aquarium Research Institute in California, wrote in an email to Eos. Paull was not involved in the new study.
However, the study’s results tell a different story. “The paper shows for the first time that there are fundamental differences between the processes that form [terrestrial and submarine canyons],” Paull noted.
In the new study, researchers compared the channel concavity and steepness indices of 23 terrestrial and 29 submarine catchments. Overall, the concavity indices were lower for submarine canyons than for those found on land. In addition, the tributaries in submarine formations were steeper than their associated main stem, but land-based tributaries and main stems were similarly steep.
On land, significant changes in canyon shape are often triggered by large flood events or landslides. Under water, the processes that form canyons may be periodic landslides from extreme steepness, seismic activity, or large winter storms that funnel sediment from the shallow continental shelf, researchers explained in a statement.
“I think this study does a very nice job of concisely testing and expanding the quantitative approach to submarine channel networks. I’m pleased that these questions are becoming more tractable and am intrigued by the results,” Michael Elliot Smith, an associate professor at Northern Arizona University in Flagstaff, wrote in an email to Eos. (Smith wasn’t involved in this study but was on Dobbs’s master’s degree committee.) “Hopefully, this kind of approach will further convince the global research community of the importance of acquiring more high-resolution bathymetries from more submarine systems.”
Looking Ahead
The recent work “gives us the ability to effectively fingerprint different drainage sites,” including extraterrestrial sites, Dobbs said. This type of fingerprinting could serve as a proxy for studying how the canyons, channels, and other features found on Mars’s landscape formed.
New insights about canyon formation are also useful back on Earth, of course.
“The full exploration of concavity factor for a large subset of canyons yields another important difference between terrestrial and marine systems,” Smith said. “It’s very exciting to see this particular detail come into focus, and [I] hope more people get involved with the overall inquiry about marine incision in the future. To me, marine geomorphology is as exciting, or even perhaps more so, [as] the exploration of Mars.”
—Rachel Crowell (@writesRCrowell), Freelance Science Journalist