MARINE GEOLOGY (GEOL 5533) - Fall 2001

LABORATORY 1 - OCEAN BASIN GEOMORPHOLOGY

Due 17 September 2001

For this lab, we will investigate the geomorphology of the world's ocean basins in a most traditional manner - indeed, in the same manner that geologists historically learned about the seafloor - through examination of the bathymetry (depth) of the oceans. However, our method for examining ocean basin bathymetry will rely on a decidedly late 20th Century innovation - the Internet and World-Wide Web. Using the map on pages 32-33 of your text, locate the following seafloor areas:

Once you have located these sites, go to the World-Wide Web and visit the National Geophysical Data Center (NGDC), Marine Geology & Geophysics Division (MG & G). At the bottom of their home page:

1. click on the "Bathymetry & Global Relief" link;

2. click on "Global Relief (bathymetry/topography)"

3. click on "Search Gridded 5-minute Global Relief Data "

This page permits access to a database of global elevation and bathymetry which can be downloaded to your PC and used for many other applications. To access the data, you need to query the database by entering a latitude/longitude window. This window can be of any rectangular or linear dimension. For our purposes, we want to be able to examine bathymetric profiles from our chosen localities. As such, I have tried to give you profiles that run either north-south or east-west over interesting features of the ocean basins.

Follow the instructions for entering lat-lon coordinates for each of the areas in the table above into the appropriate search window. Note the West longitudes and South latitudes must be entered as negative numbers!

1. Under "Database options", choose the default, ETOPO5 5-minute grid. (If you want to see how these data were derived, follow the ETOPO5 hyperlink.)

2. Under "Data output options", choose ASCII Format, Lat Lon Datavalue

3. Under "Delimiter" choose "Tab"

4. Click on "Create File" button

The database will search for all entries within the rectangle (or line) you have specified. When it is complete, the program will provide you with a summary of your search detailing your lat-lon window, the units of your data values, the type of delimiter for the file, the grid size and number of entries, and a description of the data stream. It also informs you that a file has been created and provides you a name and hyperlink to your data. Right click on the hyperlink and choose "Save Target As", then follow the dialogue instructions to download the file to your local disk or folder.

Start Microsoft Excel. When Excel has finished loading, choose "File Open" from the Excel menu bar. Your file is an ASCII text file (i.e. it has a .txt extension), so you will need to choose that type from the "File Types" block on the "File Open" dialogue box to see it on your disk or folder. Choose your file and it should load into Excel. Your data should paste directly into the spreadsheet. In most cases, your data will load into Excel as text and you will need to parse the data into columns in the spreadsheet. To do this, select column A in the spreadsheet. Then choose "Data" from the Excel menu bar at the top of the screen, and then choose "Text to Columns" option. When the dialogue begins, click on the "Delimited" button and click on "Next". When the next dialogue box appears, click on the "Tab" box for the delimiter, then click on the "Next" button. Finally, choose the "Finish" button and your file should take all items from column A and place them in columns A, B, C labeled Lat, Lon, Depth. Next select either the latitude or longitude column along with the depth data and create a scatter plot with a line connecting points of the data. This is effectively a topographic profile across each feature so you can see its form in the same manner we would create topographic profiles in General Geology labs.

Repeat this process for each of the seafloor features listed in the table on your lab assignment. When you make your graphs, give some consideration to both the vertical and horizontal scales. Try to create graphs which have similar scales so you can compare features directly. For example, plot the Himalaya/Tibetan plateau profile at the same scale as the Marianas Trench/Arc profile. You will be amazed!

Be prepared to turn in your profiles next week.