663 



becomes more dense, and sinks. For some time, a square root 

 relationship between age and depth of the seafloor has been 

 understood as a manifestation of the diffusion process, which 

 conducts the heat into the overlying ocean. However, the 

 accuracy of seafloor depth data and ambiguities in the age of 

 the topography (available from magnetics data) have resulted in 

 numerous hypotheses of spatial and tectonic variations in the 

 cooling process. The availability of these highly accurate and 

 finely sampled data would allow, for the first time, a detailed 

 study of the spatial variations in this important evolutionary 

 process. 



The oceanic iithosphere acts as an elastic plate of time- varying 

 thickness. As Iithosphere ages, volcanoes are sometimes 

 erupted onto the plate (e.g., Hawaii) and the loading causes the 

 Iithosphere to flex. Often such flexure results in moats around 

 the volcanoes, and the spatial characteristics of the flexure can 

 be used to estimate the thickness of the plate and the age of 

 loading. Frequendy the Iithosphere can be reheated after 

 cooling: previously submerged islands can again ascend above 

 the ocean's surface. Outward of oceanic trenches, old, cold 

 Iithosphere is flexed by the forces associated with the subduction 

 of the Iithosphere to great depths. Again the spatial characteristics 

 can be used to provide an estimate of the elastic thickness. 

 Detailed ocean bottom topography, enhanced by geoid and 

 gra\ ity data, would greatly expand upon the data sets available 

 for studying the importance of the elastic Iithosphere in 

 understanding the vertical component of tectonics in the oceans. 



The North Pacific contains many linear volcanic chains that are 

 poorly defined on current bathymetric charts. Most scientists 

 believe that these chains formed as the Pacific plate moved over 

 numerous hot spots. However, some chains may be caused by 

 volcanism associated with plate deformation. High-resolution 

 bathymetry would help address this issue by revealing the 

 spatial relationships among the volcanoes. Moreover, high- 

 resolution maps would reveal the detailed morphology of 

 individual structures. The important morphological features 

 are the flatness of the seamount or guyot, the number of rift 

 flanks, and preferential alignment of the rift flanks perhaps 

 related to plate-wide stress patterns. Finally, detailed bath- 

 ymetry is needed for magnetic modeling of individual 

 seamounts to establish their paleolatitude of formation, as well 

 as magnetic reversal patterns along volcanic chains. 



The Navy's bathymetry data are truly a national asset. The 

 compilation and gridding represents an estimated 176 man- 

 years of effort, and the sur\ ey data on which the data are based 

 are never likely to be duplicated. Accurate and detailed 

 measurements of the ocean depth can only be done using ships, 

 which is both expensive and time consuming. 



Raw, side-scan sonar data offer an exciting opportunity to 

 augment relatively low-resolution sur\eys, which have been 

 available for several years in limited areas (p. j.. GLORIA). The 

 availability of high-resolution side-scan sonar coverage will 

 have major implications for the oil and gas industry in mapping 

 seafloor faults and fractures that control oil or gas seeps, 

 produce subsea freshwater springs, and contribute to slope 

 instability. Hazards to navigation and existing pipelines can be 

 much more accurately located, facilitating pipeline repair or 

 ship routing around hazards. 



d. Findings 



The findings relative to marine bathymetry are: 



• The joint availability of magnetics and seafloor topography 

 data, in combination, would greatly improve the accuracy of 

 plate tectonic reconstructions and materially aid planning of 

 at-sea experiments and a variety of ocean measurements and 



analyses. 



• It is very important that the Navy's planned release of 

 DBDB-V is achieved soon. 



• A determination should be made concerning the level of 

 utihty afforded by DBDB-V if significant amounts of the 0.5 

 arc minute resolution database (DBDB-0.5) are not released 

 and incorporated into DBDB-V. 



• Provided that the release of DBDB-V occurs, there will be a 

 smaller potential scientific benefit to the release of the 

 remaining classified data. However, should the plarmed 

 release of DBDB-V with 0.5 arc minute data not occur, we 

 strongly believe that a review of the classification policies 

 themselves should be undertaken with a view toward making 

 such a declassification possible. 



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