Dive into Bathymetry: Discovering the Secrets of the Seafloor

1. Labs Start Next WeekDon’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

2. Shape of the SeafloorChapter 2

3. Techniques of Bathymetry - 1 • Challenger expedition (1872-1876) -1st systematic bathymetric survey • ocean floor not flat - significant topographic relief • German ship Meteor (1920’s) - 1st echosounding survey • sounds travels through water much better • velocity = distance/time • SONAR (Sound Navigation and Ranging)

4. Bathymetry - 2 • WWII - U.S. Navy further developed SONAR technology • knowledge of the enemy • knowledge of the ocean • 1950’s - 1960’s - single, focused high-frequency, short wavelength sound beam • “wide-beam” bathymetry • sound beam spreads out as it reaches bottom • range of depths - fuzzy estimate

5. single, focused high-frequency, short wavelength sound beam

6. 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

7. multiple, focused, high-frequency, short wavelength sound beams A Gigabyte of data an hour A Gigabyte of data a day

8. Bottom Coverage & Data Density by Survey Method Leadline Single Beam Multibeam 1-2 K soundings per survey 500 - 750 K soundings per survey 400,000 – 1,000,000 K soundings per survey Image courtesy of NOAA & UNH

12. N

13. N

17. Shallow Water Multibeam

18. Shallow Water Multibeam (cont.)

19. Tutuila Surveys

22. Tutuila Surveys

23. Fagatele Bay National Marine Sanctuary

24. FBNMS Benthic Habitat

25. Need for Mapping Oregon Territorial Seafloor Siletz Bay Goldfinger et al., OSU Active Tectonics & Seafloor Mapping Lab Oregon Department of Fish & Wildlife

26. Applications for Mapping

27. dusk.geo.orst.edu/3mile/consensus_statement.pdf

28. “Fine Scale” Mapping • on the order of tens of meters to meters • features the size of a can of beer!

29. Study Area Image courtesy of Dan Fornari, Woods Hole Oceanographic Institution

30. 2005 HURL Sub & ROV surveys Ka‘imikai-o-Kanaloa Pisces IV or V HURL = Hawaii Undersea Research Lab ROV= remotely-operated vehicle RCV-150

31. 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

32. Sidescan Sonar Image courtesy of USGS Woods Hole

33. DSL-120 Vehicle Image courtesy of WHOI Deep Submergence Lab and Dr.Dan Fornari Image courtesy of USGS Woods Hole

38. 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

40. 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 sediment-laden water • deepsea fans • continental rise • abyssal plain - extensive, flat

42. 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

44. Seafloor Features: Deep Ocean • Plate Boundaries • Ridges (Rises), Trenches, Transform Faults, Fracture Zones