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INSIDE SUBMARINE VOLCANIC ERUPTIONS Using voxels to reveal anomalies
Neeti Nayak and Keith VanGraafeiland, Esri
Point turbidity measurements collected by the sensors on Kilo Moana, showing the different submarine volcanoes.
The innate interdisciplinary nature of GIS demands that the results of a complex multidimensional data analysis should lend itself to digestible vi- sualization with interactive tools for visual analytics. Voxel layers, which represent multidimensional spatial and temporal information in a 3D vol- umetric visualization, provide GIS users with a highly accurate volumetric analysis and an understanding of conditions and phenomena that can't be physically experienced.
Most of the volcanic activity on Earth occurs on the ocean floor. For exam- ple, the floor of the Lau Basin, located in the southwest Pacific Ocean, is one of the most volcanically active areas known to scientists. Exploration of Lau Basin by the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory (PMEL) Vent Program in 2008–2010 revealed numerous locations of hydrothermal activity and two active eruptions. Water quality characteristics were collected and mapped to better understand the range of the erupting undersea volca- noes, explore the spatial extents of volcanic ash plumes, and recognize the global impacts of submarine eruptions on ocean chemistry. The data in- cluded measurements collected by a conductivity, temperature, and depth (CTD) device, which was towed by the research vessel Kilo Moana.
The CTD device was raised and lowered through the water column while passing over active hydrothermal vents. The device collected temperature, conductivity, salinity, and turbidity measurements so that researchers could precisely determine the shape of hydrothermal volcanic plumes and source locations on the ocean floor.
NOAA/PMEL in Seattle, Washington, recorded tabular data representing locations in the north Mata project area (where turbidity anomalies were observed) and mapped the data as points. Using turbidity measurements taken above the erupting undersea volcanoes, the program performed a 3D geostatistical interpolation to predict turbidity levels throughout the study area. The results were exported to a multidimensional data file (in NetCDF format) for viewing as a voxel layer in GIS.
The voxel layer reveals anomalies, specifically high turbidity values cor- responding to eruptions and the structure and symmetry of the different eruptions. Particle anomaly contour plots from CTD tows and the corre- sponding voxel visualization of the erupting peaks, along with a section diagram showing the voxel dissected into planes, show the distribution of turbidity values within the volume.
Interpolated voxel layer from the point data, showing the different submarine volcanoes.
Data provided by the NE Lau Basin, R/V Kilo Moana expedition KM1008, April 28–May 10, 2010, cruise report.
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