Hydrothermal activity is one of the dominant processes affecting the chemical and thermal evolution of oceanic crust at the mid-ocean ridge (MOR), but little is known about the sub-surface portions of ridge hydrothermal systems. These systems can be investigated using numerical modeling techniques, and models of two-dimensional cross-sections are utilized in this study to investigate the behavior of MOR hydrothermal systems. The influence of magma chamber geometry is explored by modeling two extremes of proposed geometry. Seismological evidence supports a dike-like 2 km half-width chamber, and models of this chamber indicate that: (1) complete crystallization of the magma requires 30,000 years, (2) hydrothermal upflow and hot springs are concentrated in a narrow band within 1.5 km of the ridge axis for the lifetime of the system, (3) a large hydrothermal cell forms and remains centered above the distal tip of the intrusion for the lifetime of the system, (4) effective hydrothermal activity ends by 70,000 yrs. Petrological evidence supports a wide sill-like chamber 15 km in half-width, and models of this chamber indicate that: (1) complete crystallization of the magma requires 100,000 yrs, (2) hydrothermal vents are present at the ridge axis, but most of the vents are located 5-10 km away from the axis, (3) a large hydrothermal cell develops at the distal tip of the magma chamber, while a series of small but vigorous cells develops directly above the intrusion, both features migrate toward the ridge axis as the magma solidifies, (4) effective hydrothermal activity ends by 170,000 yrs. Substantially different hydrothermal systems develop around these two chamber geometries and comparison of the models shows this is because different patterns of near-critical P-T conditions developed around them. The fundamental influence on the nature and pattern of hydrothermal circulation at MOR is the distribution of near-critical conditions.

This project aimed to constrain the interpretation uncertainties associated with reflection seismic data of deep-water slope deposits.  The basic premise of the project is that seismic data is affected by small-scale architectural elements and even conventional low-frequency data may contain clues of the sub-seismic geometries.  These can be decoded by understanding the interaction between internal elements and the seismic wavelet.  A series of outcrop-derived forward seismic models was created, representing different types of outcrop based slope deposits.  The seismic interpretation of the forward models was based on amplitude analysis supplemented by instantaneous attributes and spectral decomposition. In order to create realistic synthetic seismograms, input models included geometries whose thickness was as low as 1% of the resolution limit.  By revealing the influence of small-scale structures on synthetic seismic data at the high end of the spectrum (70Hz to 100Hz), the knowledge of tuning effects and the interaction between interfering reflections at lower frequencies (i.e. 20, 40 and 60Hz) could potentially be significantly improved. The gained experience was then applied to real seismic data.  It was proven that small-scale geometries have an additional, highly significant effect on the composite reflection. Because of the inherent non-uniqueness in seismic reflection, the specific seismic forward models of particular outcrop analogues can only be used as guides to the seismic interpretation of the particular architectural elements of a subsurface deposit and not as definite models against which one can definitely pattern match real and modelled seismic data.  as burial depth increases, so does the non-uniqueness of the seismic interpretation of seismic data from deposits whose internal geometries are around/below the tuning thickness.

Approved for public release; distribution is unlimited / Naval operations are highly dependent upon environmental conditions that can either adversely affect successful completion or hinder the safety of personnel. Each warfare community has defined environmental thresholds and operating limits that restrict the execution of any intended maneuver. As the warfare environment continues to shift from open ocean to the littoral, environmental prediction and modeling efforts of the shallow water surroundings need to be developed in order to support these operations. A hydrodynamic model, Water Quality Management and Analysis Package (WQMAP), has been developed by Applied Sciences Associates, Inc. that is designed specifically to provide accurate littoral environmental prediction. WQMAP is one of several hydrodynamic models used operationally by the Naval Oceanographic Office (NAVOCEANO) to predict currents and water elevations in littoral regions. Implementations of shallow water hydrodynamic models in foreign waters are usually data-starved for model forcing and validation. In a series of studies, NAVOCEANO intends to model various bays within the continental United States, where sufficient data exists, to study the sensitivity of lack of data on model results. This study will utilize WQMAP to design a hydrodynamic model in San Diego Bay to predict currents in order to investigate the impact of grid resolution on model results, and to provide proper current predictions for Fleet training and operations. / Lieutenant, United States Navy

Accurate prediction of nearshore waves and currents is of critical importance in littoral naval operations. This study examines the effects of complex bathymetry on nearshore currents. Data collected by an array of 12 pressure and velocity sensors in the Nearshore Canyon Experiment (NCEX), conducted near La Jolla, California in 2003, were analyzed to investigate the variability of nearshore currents near a submarine canyon. Time series of pressure, 3-component velocity, and wave heights along the 10 meter depth contour were analyzed to determine the relative importance of tides, waves, and winds in the forcing of nearshore currents outside the surf zone. Additionally, the spatial variability of the observed currents was investigated in relation to the nearby canyon head. Case studies are examined to determine how different wave and tide conditions affect the currents near the canyon. In low-moderate wave conditions, tides dominate longshore currents, whereas cross-shore currents show the passage of irregular bore-like features. The currents are coherent away from the submarine canyon and decay towards the canyon head. Strong longshore currents were observed near the canyon head during a large wave event that were likely driven by an alongshore pressure gradient associated with wave set-up variations.

This research concerns the design and analysis of different Side-Looking Sonar experiments in order to satisfy different operational requirements. The different designs and analysis have been done via computer simulation. Side-Looking Sonar (also known as side-scan sonar) is known for very high quality, high resolution, ocean bottom imaging. Hence, it is used for bathymetric surveys, commonly called seafloor mapping. It is able to rapidly survey large ocean areas for bottom and suspended sea-mines or other kinds of threats. Another operational aspect of these systems is that they allow autonomous underwater vehicles (AUVs) to conduct operations, mostly in shallow water and near land. Thus Side-Looking Sonar can be a very useful device in littoral warfare operations. This research has defined the basic parameters that rule the operation of a Side-Looking Sonar and, furthermore, analyzed various aspects that affect the performance of these parameters. Special focus was given to the various operational requirements and conditions that a designer or a user may encounter in realistic situations. Toward that end, many numerical examples are presented. Moreover, the research has tried to indicate the various problems that may arise when a Side-Looking Sonar operates in its near-field region and suggests certain solutions. The active sonar equation and its factors were explained and were evaluated for a realistic example of mine detection as well.

The Navy's Impact Burial Model (IMPACT35) predicts the cylindrical mine trajectory in air and water columns and burial depth and orientation in sediment. Impact burial calculations are derived primarily from the sediment characteristics and from the mine's three-dimensional air and water phase trajectories. Accurate burial prediction requires that the model's water phase trajectory reasonably mimics the object's true trajectory. In order to determine what effect varying the shape to more closely match real-world mines has on the shape's water phase trajectory, Mine Drop Experiment II was conducted. The experiment consisted of dropping four separate types of scaled shapes (Sphere, Gumdrop, Manta, and Rockan) into a water column, and the resultant falls were filmed from two nearly orthogonal angles. Initial drop position, initial velocities, and the drop angle were controlled parameters. The Sphere and Gumdrop shapes tended to have smooth arcing drop paths. The Manta shape dropped much more slowly than the Sphere or Gumdrop shapes. The Manta had a tendency to either fall in a spiral with its bottom parallel to the bottom or on its side in a twisting motion. The Rockan tended to either flip or swoop as it entered the water but then settle in a slow spin with its primary length parallel to the bottom. The dispersion of all four shapes at the selected depth of 2.5 m was wide and variable. The data collected from the experiment can be used to develop and validate the mine Impact Burial Prediction Model with operational, non-cylindrical mine shapes.

Approved for public release; distribution is unlimited / This analysis addresses the value of a submarine base in the Arctic in relation to the growing Soviet threat in that region and the feasibility of constructing and operating such a submarine base. Location, command and control, force operation, logistic support and appropriate force size are elements of the analysis. Also included is the cost effectiveness of the Arctic submarine base both in peacetime and in wartime situations. Based upon this limited analysis, such a base appears to be only marginally cost effective in peacetime but substantially so in wartime. / http://archive.org/details/analysisofbuildi00best / Lieutenant, United States Navy

No description available.

The topic of this thesis is the study of deposits from ancient submarine channel systems in the Miocene Maraş Basin (southern Turkey). The results show four independent systems in the form of slope channel complexes in the stratigraphic sequence of the basin. The present study focuses particularly on the reconstruction of the sedimentary architecture and palaeo-flow interpretation of the deposits of two of these systems: the Alikayası and the Karışık Systems. The approach followed was the architectural analysis scheme. The data from maps, sketches and logs was organized following a hierarchy of bounding surfaces as well as by the grouping of canyon/channel-fills according to key sedimentary attributes. The resultant sedimentary architecture of the Alikayası System suggests a fundamental control by the propagation of a submarine fold-and-thrust belt. The sedimentary architecture of the Alikayası System does not agree with generic hierarchical models proposed for the description of slope channel complexes. On the other hand, the Karışık System is interpreted as an intraslope system, which was dominated by submarine landslides and developed small channel systems, resulting in sequences of mass transport deposits and channel-fills. The propagation of a fold-and-thrust belt also controlled the sedimentary architecture of the Karışık System. All the systems identified in the Maraş Basin are interpreted to have been part of submarine channel systems connected to the shelf, transferring coarse-grained clastic sediments (e.g. gravel and sand) from the coast to the marine deepwater environment.

Monowai is an active submarine volcanic center in the Kermadec Arc, Southwest Pacific Ocean. We show, using cross-correlation and time-difference-of-arrival techniques, that low-frequency underwater sound waves from the volcano travel in the Sound Fixing and Ranging (SOFAR) channel and can be detected by bottom-moored hydrophone arrays of the International Monitoring System (IMS), a global sensor network maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization. Hydroacoustic phases associated with the May 2011 eruption at Monowai are identified in the record of the IMS station at Ascension Island, Equatorial Atlantic Ocean. The source-receiver distance of ~15,800 km is the furthest documented range of any naturally occurring underwater signal ever observed. Our observations are consistent with results from transmission loss modeling, which suggest that acoustic propagation at southern latitudes is facilitated by the anomalous temperature regime of the Antarctic Circumpolar Current. Subsequently, we examine the 3.5-year record of the IMS hydrophone station near Juan Fernández Islands, Southeast Pacific Ocean, for volcanic activity at Monowai. Density-based clustering of arrivals during the time periods when data is available, i.e. from July 2003 to March 2004, and between April 2014 and January 2017, reveals 82 discrete episodes that are spaced days to weeks apart, typically ranging from a few hours to days in length. The resolution of the hydrophone data for seismic events at the volcano is estimated at 2.2 m_b and exceeds regional broadband networks by one order of magnitude. Considering the results and techniques developed in the study of Monowai, we investigate the 2014 submarine eruption of Ahyi volcano in the Northern Mariana Islands. Acoustic phases of the 15-day episode are identified in the record of an IMS hydrophone array located at Wake Island in the northwestern Pacific Ocean. Explosive volcanic activity occurred in two bursts, accompanied by a decrease in low-frequency arrivals that is interpreted as a shift in signal source parameters. Acoustic energy released during the event is on the order of 9.7 10¹³ J.