Copy of GS108 Lab 2 Geology of the Seafloor

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School

Linn Benton Community College *

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Course

108

Subject

Geology

Date

Feb 20, 2024

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pdf

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8

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Name ______ Sage Clark ______________ Lab 2—Geology of the Seafloor GS108 Key Ideas To become familiar with seafloor bathymetric features and their relationships to tectonic boundaries. Objectives a) Identify seafloor features such as seamounts, ridges, trenches, and abyssal plains b) Calculate seafloor spreading rates c) Compare and contrast relief of mountains on the seafloor and on land Procedure This lab has one part. ● Part 1: You will use the NOAA Ocean Digital Atlas online mapping tool to locate and identify geologic features of the Atlantic Ocean Basin. ● Part 2: You will calculate seafloor spreading rates at two locations in the Atlantic Ocean and determine a reason for why they are different. ● Part 3: You will use the NOAA Ocean Digital Atlas online mapping tool to locate and identify geologic features of the Pacific Ocean Basin. ● Part 4: You will compare and contrast the elevations of Mauna Kea and Mt. Everest. Submission Please submit a PDF to Moodle by Sunday at 11:59 pm. Criteria This lab is worth 10 points and will be graded using a rubric on Moodle. 1
Background What do you imagine is on the bottom of the deep ocean floor? Do you picture it as a big, smooth bathtub with green slime on the bottom and perhaps a few giant fish swimming around in the dark, freezing cold? The ocean floor has this and more! In fact, all of the major landforms that we find on the continents (mountains, valleys, plains, gigantic canyons, etc.) are found on the ocean floor as well. It is anything but smooth! Mountains Under the Sea There are 2 common types of mountains on the seafloor, both volcanic: mid-ocean ridges/rises and seamounts . Mid-ocean ridges are long, linear volcanic ridges formed where the seafloor fractures into 2 plates of oceanic crust that spread away from each other. The cracks between the diverging plates of lithosphere are filled with magma that rises from the mantle beneath mid-ocean ridges, and solidifies into new oceanic crust along the crest of the mid-ocean ridge. Repeated cycles of cracking, spreading, melt injection, and solidification of new crust along mid-ocean ridges over long periods of time (tens to hundreds of millions of years) produces large plates of oceanic lithosphere that floor entire ocean basins. For this reason, we say that the seafloor is "born" or "created" at the mid-ocean ridges. Rises have gentler slopes and are not as steep. Seamounts Seamounts are submerged volcanoes on the seafloor. They may be active or extinct, and may occur as isolated peaks, as groups, or as linear chains. These regions of activity may be associated with mid-ocean ridges, as is the case with Axial Seamount to the left (source: NOAA), with hot spots in the mantle (as is the case with Loihi Seamount, which will one day become the newest island of Hawaii). 2
Other Features Under the Sea: Trenches, Fracture Zones, Abyssal Plains Subduction zones are places where an oceanic plate is bending down into the mantle and sinking (subducting) beneath another oceanic or continental plate. A very deep trench is formed parallel to the zone of collision. Here in the Pacific Northwest, there is the Cascadia Subduction Zone that separates the Juan de Fuca Plate from the North American Plate. We also have the Juan de Fuca Ridge, a spreading center or mid-ocean ridge near us, acting as the boundary between the Juan de Fuca Plate and the Pacific Plate. (Image: Oregon Department of Geology and Mineral Industries) In referring to mid-ocean ridges and subduction zones we have really been talking about major plate tectonic boundaries. Mid-ocean ridges are places where new plates are formed and subduction zones are places where plates are destroyed. A transform fault is a third type of plate boundary. This is where plates slide past each other. The San Andreas fault in California is such a place (see USGS photo, left). Or on a more detailed scale, portions of the mid-ocean ridge are often separated by smaller transform faults that form where the diverging plates are slipping laterally past each other. The rugged topography resulting from the deformation of the seafloor along transform faults is carried away with the spreading plates and forms inactive extensions of the transform faults, called fracture zones . The seafloor also has huge, flat, deep areas where sediments have buried the rough volcanic terrain that was created at mid-ocean ridges. These places are called abyssal plains . In this lab, you will use a very beautiful map that depicts what Earth would look like if all the water were drained out of the oceans. The map will show you all the above features. Study the map carefully and answer the questions below. 3
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