Scientists have now mapped the seafloor around the Hunga Tonga-Hunga Ha‘apai volcano, and as a result we have learned just how massive the January 2022 eruption was. By comparing their soundings with 2017 data, they determined that at least 9.5 km³ of material was discharged. Debris was found 80 km from the volcano, and the volcano’s caldera has been replaced by a cavern 850 m deep. More from the NIWA media release and from ABC (Australia).

Previously: Remotely Operated Vessel Maps Tonga Caldera.

In their paper, the complete text of which is available online, physical geographer Simon Haslett and professor of Celtic David Willis are trying to reconstruct the post-glacial evolution of Wales’s Cardigan Bay using historical and folklore sources as well as bathymetric data and geological evidence. (It’s pretty obvious which author contributed what.) The Gough Map shows two islands that don’t correlate to any real island in Cardigan Bay; the study suggests that the islands may have in fact existed and have since been lost to flooding, erosion and other post-glacial changes to the shorelines. There are several submarine highs in the bay that may match up with the lost islands. The paper hypothesizes that the Cantre’r Gwaelod legend is a folk memory from when the coast was much different: that there were islands in Cardigan Bay, that they disappeared during the human era, and this legend is one of their traces.

In other words, a bit different from taking an old map at entirely too much face value (which, to be sure, has been enough of a thing that it was first to mind when I saw the story). They’re using the map and the legend to try and figure out the shoreline’s history—not using the map to prove the legend.

As part of the Tonga Eruption Seabed Mapping Project, a robotic vessel has conducted a bathymetric survey of the Hunga Tonga-Hunga Ha‘apai volcano’s underwater caldera. Said volcano, you will recall, erupted spectacularly last January. The 12-metre vessel, USV Maxlimer, was controlled remotely from 16,000 km away, and carried sensors to measure the state of the seabed, temperature, salinity, turbidity, dissolved oxygen and chemical plumes. More at the press release. BBC News coverage.

Previously: The Rise and Fall of Hunga Tonga-Hunga Ha‘apai; Hunga Tonga-Hunga Ha‘apai, Before and After; How Satellites Revealed the Hunga-Tonga Hunga-Ha‘apai Eruption.

Kara Prior cross-stitches earth science maps; her work includes a series of state bedrock geology maps (see also Reddit) and a bathymetry map of the Great Lakes (above), among other things. She has an Etsy store.

NASA Earth Observatory summarizes recent work in using satellite data to improve our maps of shallow seafloors—where the situation changes more often than traditional sonar methods can track—by, among other things, using a laser altimeter system on one of NASA’s satellites.

In 2021, Nathan Thomas and Lola Fatoyinbo of NASA’s Goddard Space Flight Center, along with colleagues from three countries, took another step by mating ICESat-2 measurements with images from Copernicus Sentinel-2 to derive bathymetry at better resolution. The team mapped the shallows down a depth of 26 meters (85 feet) around Biscayne Bay in Florida, the Gulf of Chania in Crete, and the island of Bermuda.

Thomas and colleagues compared their satellite-derived bathymetry with maps made from traditional topographic surveys, multibeam sonar, and nautical soundings. Their new maps had a resolution of 10 meters, improving upon the current 115-meter resolution dataset for Crete and the 30- to 90-meter datasets for Florida and Bermuda. The existing data for Florida and Bermuda are composites of lots of sources spanning 63 years, while the ICESat-2/Sentinel-2 maps offer a contemporary assessment of underwater structure.

See also this earlier Earth Observatory item from last year. (Deep water bathymetry is another thing: light can’t get down that far. But out-of-date soundings are less impactful on shipping.)

The Australian government has released high-resolution sea floor map data of the Great Barrier Reef; the data improves the view of the relief by a factor of eight, from 250-metre resolution to 30-metre resolution. The result of a collaboration between James Cook University, Geoscience Australia and the Australian Hydrographic Service, the data “can be used for policy, planning and scientific work. For example, this data is an important input for oceanographic modelling, which we can use to enhance our knowledge of climate change impacts, marine biodiversity, and species distribution.” Press release, data files.

To date, more than 85 percent of the seafloor has not been mapped using modern methods. Since 70 percent of the Earth is covered in oceans, this means that we quite literally don’t know our own planet. “We know the surface of Mars better than we do the seafloor,” says Martin Jakobsson, a researcher at Stockholm University.

[Leventhal/MAPS-L]

New seafloor maps of the Monterey Bay area have been released as part of the California Seafloor Mapping Program. The maps “reveal the diverse and complex range of seafloor habitats along 130 kilometers (80 miles) of the central California coast from the Monterey Peninsula north to Pigeon Point.” [Leventhal Map Center]

Previously: Mapping the California Sea Floor.

The USGS‘s California Seafloor Mapping Program has produced a set of insanely detailed maps of the sea floor along the California coast. Downloadable as rather hefty PDF files; the map sheets are three feet across as paper maps. Above, a detail from the shaded-relief bathymetry map of the San Francisco area. Boing Boing, Wired.