Hawaiian volcanism is understood on land, but what, when, and how lava erupted in the ocean depths surrounding the islands is a mystery. This expedition (officially'KM0718') will survey and sample rocks from huge volcanic fields surrounding the Kaua'i, Ni'ihau, and Ka'ula. A major target is a topographic bulge, which extends south from Kaua'i, is broader than Kauai itself, and is unlike any feature around the other islands. This bulge is covered with many tens of volcanic mounds and pinnacles roughly the size of the famous Diamond Head crater in Honolulu. There are hints that these features continue to punctuate the seafloor south of Ni'ihau and around the west and north side of Ka'ula. Scientists know these volcanic features are no longer active but they do not know whether they formed during the main (shield) phase of volcanism on the islands or whether they formed more recently, in a manner similar to Diamond Head. State-of-the-art sonar equipment will map these features and we will use the submarine robot JASON2 to take photographs and sample the rocks. The rocks will be analyzed to determine when they erupted, how hot they were, what they are composed of, and with what stage of Hawaiian volcanism they best fit. All of this information will reveal new secrets about submerged volcanic activity around the northern Hawaiian Islands.
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"Multibeam" sonar will be used to map the "bathymetry" (which means under water topography) of the seafloor and volcanoes (see colored map above). Multibeam means that an array of sonar beams are emitted from the ship, reflected at different parts of the seafloor, and then recorded by very sensitive hydrophones. The time it takes sound to travel down and back up from each location of the seafloor is used to determine how deep the seafloor is. The use of multiple beams allows a whole swath of seafloor depth to be collected, thus allowing the Kilo Moana to "paint" an image of the seafloor as it surveys.
The same concept will also be used to collect "side-scan" sonar data (see dark shading in insets of map above). Instead of measuring seafloor reflection depth, side-scan sonar measures how loud the seafloor echo is. In so doing, we can remotely sense whether the seafloor is acoustically hard - as would be volcanic rock - or whether it is acoustically soft - as would be soft mud overlying the volcanoes. See the Hawaii Mapping Research Group (HMRG) web site for more information about sonar mapping.
The geophysical measurements include gravity and magnetics. Our shipboard gravimeter is an extremely sensitive instrument that measures minute changes in how hard the Earth’s gravity is pulling. These subtle (millionths of the total strength) variations occur everywhere on Earth and are caused by variations in the density of rock below us. In our survey region, gravity variations will help us find where dense magmatic intrusions or where less dense eruptions occurred. The magnetometer measures very small variations in the Earth’s magnetic field, caused by weakly magnetic rocks. These rocks are weakly magnetic because they contain a lot of iron and the patterns of their magnetization tell us when the rocks formed.
(Image credit Woods Hole Oceanographic Institute)
The investigation will focus on detailed surveys by a submarine robot, JASON2, which is operated by the Woods Hole Oceanographic Institution (WHOI). We will use JASON2 to take video and still images of the rocks and use JASON2's mechanical arms to take rock samples. JASON2 is our way of doing underwater geology in water depths of 1-3 miles deep!
(Image credit WHOI)
More information about JASON2, see the WHOI web site.
About the R/V Kilo Moana
R/V KILO MOANA has a twin hull design to provide a comfortable, stable
platform allowing general purpose oceanographic research in
coastal and deep ocean areas, even in high sea states. She has
the speed (15 kts max; 12 kts survey), endurance (50 days),
payload (100 LT) and range (10,000 nm) to operate
throughout the Pacific and indeed globally. Dynamic positioning
(with twin screws and bow-thruster), differential
GPS, and an integrated bridge and
power control system, permit accurate surveying and precise station