Mid-Term Exercises Part A: Ocean Bathymetry
Quiz Instructions
Tasks
The main aim of Part A of this mid-term exercise is to answer a series of questions based on compilation of bathymetric data that enable evaluation of the following hypothesis, posed as a question:
- Does subduction of volcanic ridges and seamounts change the bathymetry of deep-sea trenches?
This page also provides links to the resources, previously utilized in Module 4 and in the Phase I Group Activities, that help accomplish the task.
Resources
At the Satellite Geodesy operated by Scripps Institution of Oceanography (TopoMaps (Links to an external site.)) select the regions specified in the individual questions using the link provided.
A pdf file that presents compact versions of the four bathymetric images corresponding to each of the questions can be downloaded here.
Use this map to answer the questions that follow aided by the depth scale below.
Question 1: Locate the position on the Peru-Chile trench at approximately 15°S, 82°W in the bathymetric map of the eastern South Pacific and South America (E. Pacific (Links to an external site.)) where the Nazca Ridge meets the South American continental mainland. Compare the approximate width of the trench and its depth using the bathymetry scale to portions of the trench on either side of the Nazca Ridge and describe any differences between these locations.
A strong answer will describe the topography and bathymetry, specifically width and depth, of the Peru-Chile Trench at the target location and compare these characteristics with other portions of the trench, noting (and quantifying where possible) differences in its width and depth associated with the intersection of the Nazca Ridge.
Question 2: Locate the position on the Izu-Bonin trench at approximately 25°N, 143°E in the bathymetric map of the western Pacific (W. Pacific (Links to an external site.)) where a chain of Pacific seamounts meets the trench near the Bonin Islands. Compare the approximate width of the trench and its depth using the bathymetry scale to portions of the trench on either side of the seamounts and describe any differences between these locations.
A strong answer will describe the topography and bathymetry, specifically width and depth, of the Izu-Bonin Trench at the target location and compare these characteristics with other portions of the trench, noting (and quantifying where possible) differences in its width and depth associated with the intersection of the chain of Pacific seamounts.
Question 3: Locate the position near the junction of the Kuril-Kamchatka and Aleutian trenches at approximately 55°N, 165°E in the bathymetric map of the most northwestern Pacific (NW. Pacific (Links to an external site.)) where the chain of Emperor Seamounts meets the trench. Compare the approximate width of both trenches and their depth using the bathymetry scale at locations distant from the seamounts to the characteristics of the Kuril-Kamchatka trench where the seamounts intersect. Describe specific differences in the trenches between these locations.
A strong answer will describe the topography and bathymetry, specifically width and depth, of the Kuril-Kamchatka and Aleutian trenches at the target location and compare these characteristics with other distant portions of the trench, noting (and quantifying where possible) differences in its width and depth associated with the intersection of the Emperor Seamounts chain.
Question 4: Locate the position on the Kermadec-Tonga trench at approximately 25°S, 175°W in the bathymetric map of the southeast Pacific (SE. Pacific (Links to an external site.)) where the Louisville Ridge meets the trench south of Tonga. Compare the approximate width of the trench and its depth using the bathymetry scale to portions of the trench on either side of the Louisville Ridge and describe any differences between these locations.
A strong answer will describe the topography and bathymetry, specifically width and depth, of the Kermadec-Tonga Trench at the target location and compare these characteristics with other portions of these trenches, noting (and quantifying where possible) differences in its width and depth associated with the intersection of the Louisville Ridge.
Question 5: Bonus Question (5 pt)
Do the bathymetric data for deep-sea trenches support or refute the hypothesis that their topographic features are changed at locations where subduction of volcanic ridges and seamounts is occurring? How might these changes affect the tectonic processes associated with the process of ocean crust subduction?
A strong answer will review the topographic features of trenches observed in answering the previous questions and determine whether there is a consistent pattern of changes in the width and depth of trenches where subduction of volcanic ridges and seamounts is occurring to evaluate the validity of the hypothesis. It will also evaluate whether tectonic processes associated with subduction (e.g. rate of subduction, angle of subduction, associated arc volcanism) are likely to be influenced by the addition of crustal material.