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Labs Start Next Week Don’t forget your lab book!!! Read through labs ahead of time Exploring the Deep: GEO/OC 103 Lab Manual by Hall-Wallace et al. TA assignments now updated on web – dusk.geo.orst.edu/oceans/103labs.html Shape of the Seafloor Chapter 2 Techniques of Bathymetry - 1 Challenger expedition (1872-1876) -1st systematic bathymetric survey – ocean floor not flat - significant topographic relief ship Meteor (1920’s) - 1st echosounding survey German – sounds travels through water much better – velocity = distance/time – SONAR (Sound Navigation and Ranging) Bathymetry - 2 WWII - U.S. Navy further developed SONAR technology – knowledge of the enemy – knowledge of the ocean 1950’s - 1960’s - single, focused highfrequency, short wavelength sound beam – “wide-beam” bathymetry – sound beam spreads out as it reaches bottom – range of depths - fuzzy estimate single, focused high-frequency, short wavelength sound beam Bathymetry - 3 1970’s - revolution in bathymetric mapping with multibeam bathymetry multiple, focused, high-frequency, short wavelength sound beams – “narrow-beam” or “multibeam” bathymetry – sound beam stays narrow and focused all the way to the bottom – depths much more precise – e.g., Sea Beam has 16 beams, Sea Beam 2000 has 121, Simrad EM120 has 191 multiple, focused, high-frequency, short wavelength sound beams A Gigabyte of data a day A Gigabyte of data an hour Bottom Coverage & Data Density by Survey Method Leadline 1-2 K soundings per survey Single Beam 500 - 750 K soundings per survey Multibeam 400,000 – 1,000,000 K soundings per survey Image courtesy of NOAA & UNH Shallow Water Multibeam Shallow Water Multibeam (cont.) Tutuila Surveys Tutuila Surveys Fagatele Bay National Marine Sanctuary FBNMS Benthic Habitat Need for Mapping Oregon Territorial Seafloor Siletz Bay Goldfinger et al., OSU Active Tectonics & Seafloor Mapping Lab Oregon Department of Fish & Wildlife Applications for Mapping Tsunami Runup Models Evacuation Planning Habitat Restoration Shoreline Change Analysis Analyzing Storm Impacts Coastal Erosion Fisheries Management Commercial Fishing Marine Reserve Design Emergency Response, Impact Assessment Port Security Maps and Visualizations Navigation Products, Services Wave Energy Oil Spill Response, Tracking Coastal tourism, recreation MANY others dusk.geo.orst.edu/3mile/consensus_statement.pdf “Fine Scale” Mapping on the order of tens of meters to meters features the size of a can of beer! Study Area Image courtesy of Dan Fornari, Woods Hole Oceanographic Institution 2005 HURL Sub & ROV surveys Ka‘imikai-o-Kanaloa Pisces IV or V HURL = Hawaii Undersea Research Lab ROV= remotely-operated vehicle RCV-150 Sonar Also Used as... a “catscan” of oceans to see water structure ABOVE seafloor an “x-ray” of seafloor to see structure BENEATH seafloor – seismic reflection & seismic refraction – low frequency, long-wavelength sound sidescan sonar to get pictures of seafloor in addition to depth – backscatter strength as opposed to traveltime Sidescan Sonar Image courtesy of USGS Woods Hole DSL-120 Vehicle Image courtesy of WHOI Deep Submergence Lab and Dr.Dan Fornari Image courtesy of USGS Woods Hole Resolution with multibeam bathymetry can see things on seafloor the size of this room – swath width of 6 km or 3.7 miles good, high-resolution maps possible only since 1980’s other instruments needed to see things smaller than size of room – remotely-operated vehicles (ROVs) – submersibles Seafloor Features: Continental Margins continental shelf - extends from shore to a point marked by great increase in slope continental slope - steep slope beyond the continental shelf break slopes often cut by submarine canyons – turbidity currents - dense flows of sedimentladen water – deepsea fans continental rise abyssal plain - extensive, flat Seafloor Features: Deep Ocean seamounts - underwater volcanoes 500 m to 1000 m high – flat-topped ones are called guyots – volcanic features (buoyed up by hot rock, lava) abyssal hills - features around 200 m high – pervasive on seafloor – volcanic AND tectonic in origin - still debated Seafloor Features: Deep Ocean Plate Boundaries – Ridges (Rises), Trenches, Transform Faults, Fracture Zones