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Chapter 4 Marine Provinces Today, we're going to drain the ocean. History Posidonius: The first known to attempt at measuring the ocean's depth. (Mediterranean Sea 85 B.C.) Soundings were done by dropping weighted rope. Depth measured in Fathoms. 1 Fathom = 1.8 Meters = 6 Feet History HMS Challenger: First systematic measuring of depth. (1872) Still using rope. Notable for determining variation in ocean depth. History Echo Sounders: Early 1900's. Sends a ping to the ocean floor and records the echo. Precision Depth Recorder(PDR): WWII tech. More focused, and accurate sonar. Used in the 1960's to produce the first reliable maps of sea floor. Today Multibeam Echo Sounder: Multiple frequencies of sound used to provided detailed images. Can be attached to sides of a ship to survey sea floor (SeaBeam, 1st Multi-beam echo sounder). Side Scan Sonar: Mult-beam echo sounders towed behind the ship, provide better resolution images due to proximity to the sea floor. (Sea MARC and GLORIA) Today Satellites, like those you saw in Chapter 1, can map sea floor by measuring gravity field Echo sounding using explosions or air guns can give Seismic Reflection Profiles. <-this is where the money is, guys. Important Formula: Depth = Velocity x (Time/2) Ocean Provinces Three Major Regions: 1. Continental Margins: Shallow land close to the continents. 2. Deep-Ocean Basins: Deep land far from the continents. 3. Mid-Ocean Ridge: Shallower areas near the middle of ocean basins. Continental Margins Passive Margins: Areas that are not near a plate boundary. Characterized by low tectonic activity. Active Margins: Opposite of Passive. - Convergent Active Margins -Transform Active Margins. Continental Margins The continental margins are all characterized by the following features, in order. -Continental Shelf -Shelf Break -Continental Slope -Continental Rise Submarine Canyons Submarine Canyons: On continental slopes. They are V-shaped canyons formed by Turbidity Currents (Avalanches of accumulated sediment and rock). As the sediment and rock falls, it lands on the Continental Rise, forming a Deep Sea Fan. The Deep Sea Fan exhibits Graded Bedding. Multiple layers of graded bedding are called Turbidite Deposits. Deep Ocean Basins Abyssal Plains: Deepest, flattest land on earth. Sediments here are deposited by Suspension Settling. Peaks of the Plains: If there is a volcanic formation at least 1 Km above the sea floor, it is a Sea Mount. -If its top is flat, it is called a Tablemount or Guyot. Deep Ocean Basins Volcanic Features >1Km are called Abyssal Hills or Seaknolls. Very common feature of the sea floor. Very active areas may lack in sediment deposition, resulting in Abyssal Hill Provinces. Volcanism Flood Basalts: Large, flat surfaces of basalt rock formed by some volcanic release of magma. If found near a continent, they're called Continental Flood Basalts. Trenches Ocean Trench: Found near Ocean-Continent Convergent Boundaries. Deep scars in the sea floor where the ocean crust is subducted. Can produce a Volcanic Arc on landward side. These include: -Island Arc: Forms islands. -Continental Arc: Forms mountains on land. THE Trench The deepest point in the ocean is found in Challenger Deep, which is found in The Mariana Trench. 11,022 meters! The Ring of Fire A ring of volcanoes surrounding the Pacific Ocean Basin. Also, the majority of ocean trenches are found in the pacific ocean. Mid-Ocean Ridge World's largest land formation. Continuous, and running through all the ocean's basins. Within the center of its mountain ranges are Rift Valleys. That's where the ocean floor tears open and spits fire. Common features: Seamounts, Abyssal Hills, Fissures, Pillow Basalts, and Hydrothermal Vents. Hydrothermal Vents Formed by sea water seeping into the crust and rising back up when heated by magma. Comes in 3 flavors: Warm-Water Vents: below 30C and clear. White Smoker: 30C<T<350C. Water is white due to light colored compounds. Black Smoker: T>350C. Water is black due to metal sulfides. And one more thing! The mid-ocean ridge does not spread equally along its length. Mid-Ocean Ridges: Spread slow Mid-Ocean Rise: Spread Fast Because of this, there are many Transform Faults along it, surrounded by Fracture Zones.