Engineers map underwater marvel in the Pacific Ocean to stunning centimeter-scale

A study unleashes an ROV equipped with cutting-edge multibeam and laser bathymetry to capture an unprecedented view of a submerged 'Great Canyon.'
Sade Agard
(Left to right) A remotely operated vehicle (ROV)—Doc Ricketts—with the innovative sensor suite; Surveys shed new light on processes that sculpt submarine canyons.
(Left to right) A remotely operated vehicle (ROV)—Doc Ricketts—with the innovative sensor suite; Surveys shed new light on processes that sculpt submarine canyons.

Dave Caress/ Monica Wolfson-Schwehr 

Hidden beneath the surface of Monterey Bay is a magnificent underwater world known as Monterey Canyon. It stands as one of the largest submarine canyons along the North American west coast.

Engineers have now successfully mapped and monitored this canyon with incredible precision, down to the scale of centimeters, according to a recent study published in JGR Earth Surface

Their results, aided by an innovative sensor suite, unveil the captivating processes that have sculpted this hidden underwater marvel.

An underwater 'Great Canyon'

Though out of sight, Monterey Canyon plays a crucial role in marine ecosystems and coastal geohazards. To understand its scale, it stretches over 292 miles (470 kilometers) beneath the ocean's surface. Its widest point spans approximately 7.5 miles (12 kilometers). 

Additionally, the canyon boasts walls that rise up to 5,580 feet (1,700 meters) tall, and its deepest point lies about 2.5 miles (4 km) below the ocean's surface.

To better understand this intricate environment, researchers deployed innovative technology like the Low-Altitude Survey System (LASS), designed by Monterey Bay Aquarium Research Institute (MBARI) engineers. 

Attached to an ROV (remotely operated vehicle), the LASS utilizes cutting-edge multibeam and laser bathymetry. Essentially, as the ROV hovers 10 feet above the seafloor, it uses lasers and sonar to scan the bottom. 

Engineers map underwater marvel in the Pacific Ocean to stunning centimeter-scale
Four repeat surveys with MBARI’s LASS sensor suite between November 2015 and April 2017 provided an incredibly detailed view of the changes to the floor of Monterey Canyon.

Sonar records the seabed's structure, while lasers capture three-dimensional objects, including living creatures. After this, high-resolution photos are added to the bathymetry data, creating a realistic image of the seafloor.

"In this geological project, the lidar bathymetry data revealed changing centimeter-scale textures in the sediment on the floor of Monterey Canyon," said MBARI Principal Engineer Dave Caress in a press release.

"[These] would have been undetectable by more traditional methods like ship-based sonar or even the autonomous mapping robots we use to map at one-meter scale." 

He emphasized that despite more than 25 years of exploring Monterey Canyon, their cutting-edge technology continues to uncover unexpected discoveries.

Capturing the changes

The researchers also deployed a Seafloor Instrument Node (SIN) in Monterey Canyon, which recorded currents flowing along the canyon. 

One focus was on fast-moving turbidity currents, similar to underwater landslides, reaching speeds up to 7.4 miles per hour (11.9 kilometers/hour). These currents reshape the canyon floor, eroding and filling in features.

The surveys revealed that closer to the coast, the currents cause more significant changes in the upper part of the canyon, while their impact lessens further out to sea. 

Additionally, tides were found to play a role in shaping the seafloor, creating small scours, and altering sediment textures on a centimeter scale, which can lead to more significant changes over time.

The findings of this study not only provide valuable data for ecological studies and geological research but also contribute to understanding coastal geohazards and coastal infrastructure vulnerabilities. 

The complete study was published in JGR Earth Science.

Study abstract:

Here we show how ultra-high resolution seabed mapping using new technology can help to understand processes that sculpt submarine canyons. Time-lapse seafloor surveys were conducted in the axis of Monterey Canyon, ∼50 km from the canyon head (∼1,840 m water depth) over an 18-month period. These surveys comprised 5-cm resolution multibeam bathymetry, 1-cm resolution lidar bathymetry, and 2-mm resolution stereophotographic imagery. Bathymetry data reveal centimeter-scale textures that would be undetectable by more traditional survey methods. Upward-looking Acoustic Doppler Current Profilers at the site recorded the flow character of internal tides and the passage of three turbidity currents, while sediment cores collected from the site record flow deposits. Combined with flow and core data, the bathymetry shows how turbidity currents and internal tides modify the seabed. The turbidity currents drape sediment across the site, infilling bedform troughs and smoothing erosional features carved by the internal tides (e.g., rippled scours). Turbidity currents with speeds of 0.9–3.3 m/s failed to cause notable bedform movement, which is surprising given that flows with similar speeds produced rapid bedform migration elsewhere, including the upper Monterey Canyon. The lack of migration may be related to the character of the underlying substrate or indicate that turbidity currents at the site lack dense, near-bed layers. The scale of scours produced by the internal tides (≤0.7 m/s) approaches the scale of features recorded in the ancient rock record. Thus, these results illustrate how the scale gap between seabed mapping technology and the rock record may eventually be bridged.