What's Been Mappenin'

By the time we pull into port in Hawaii, the Okeanos Explorer’s EM 302 multibeam system will have mapped more than 8000 linear kilometers of the seafloor during the summer 2010 transit cruises to/from Guam and Hawaii. The two cruise legs followed parallel, adjacent but non-overlapping tracks in order to maximize the possibility for finding new things.

I have had the pleasure of being on board for the second transit cruise from Guam to Hawaii for the past 11 days (3 to go). Below are three of the many features of interest I spotted along the transit path. Note that the preliminary interpretations I provide here are mine alone and do not necessarily represent the views of the Okeanos Explorer or the NOAA Office of Ocean Exploration and Research.

1. Landslides

Both transits passed over a large flat-topped guyot about 500 km east of the Mariana Trench. The feature is about 20 km wide at the top and 50 km across at the base in the east-west direction. The steep-walled cliffs seem to have have been shaped by numerous landslides. Large fault scarps, slump blocks, debris aprons, and boulder fields are visible on both sides of the feature. Landslides are the second most common cause of tsunamis, so understanding the processes that lead to slope failure in the submarine environment could have important natural hazard implications.

Landslide perspective view looking towards the southwest, vertical exaggeration 3. Image Credit: NOAA.

2. Volcano

This one is my favorite. A few days ago, we discovered a small cinder cone volcano with a well-defined central crater. The cone rises about 500 meters above the local 4900-meter surface. This feature is not visible in the Smith and Sandwell bathymetry and may be a new discovery. The cone’s high degree of symmetry and lack of obvious erosional modification may indicate it is still active. Submarine hot spots that produce volcanos also form hydrothermal vents that support diverse ecosystems, so this may be worth further study. The Okeanos Explorer discovered another much larger volcano named Kawio Barat in Indonesia earlier this summer.

cinder cone perspective view looking towards the north, vertical exaggeration 3. Image Credit: NOAA

3. Paleoshorelines

About midway through the transit, we crossed the Mid-Pacific Mountains, which is a rise west of Hawaii containing a large number of seamounts, guyots, and former islands. A chain of at least four horizontal benches spanning 2-4 kilometers each is evident along the edge of one guyot. They are separated by distinct vertical drops of 200-300 meters.  These appear to be former shorelines that record the sinking of the former island. The paleoshorelines observed here likely represent the rise in sea level during the end of the last ice age, so studying them can give us clues to how climate change has happened in the past. Paleoshorelines along the continental margin of North America are thought to be important archaeological sites for discovering the ancient routes of human migrations.

Plan (A) and Profile (B) views of the horizontal benches interpreted as paleoshorelines. Image Credit: NOAA

Over the past two weeks, I've learned a great deal about how bathymetric data is collected and processed.  High-resolution bathymetry near coastlines is an important component of tsunami modeling, which is starting to play an important role in tsunami warning, so what I learn on this cruise may help me with my job at the Pacific Tsunami Warning Center.


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