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Oceanography 101 LAB 3 Saunders

Ocean Sediments & Bathymetry

Name:___________________________

1. Sediments (to be done in lab)

(1.1) At each table should be a set of sediment slides containing various sediments from around

the world. Examine the prepared sediments slides and determine their characteristics by

filling out the table below.

Slide Description Type Sorting

Oceanography 101 LAB 3 Saunders

(1.2) After you have completed the table, check your results against a key provided by your

instructor. Which sediments are more influenced by land processes (erosion, rivers, etc).

Explain.

___________________________________________________________________________

(1.3) Given what we’ve learned about sediments and their sources, would you guess that the

sediments of Puget Sound, which has 16 major and many minor rivers draining into it, are

more terrigenous, biogenous, hydrogenous, or cosmogenous? Explain.

___________________________________________________________________________

2. Core Sample

(2.1) By studying the sediments on the ocean floor, we can gather clues about what surface

conditions were like at various times in the Earth's past when the sediments were deposited.

Using those clues, we can try to reconstruct what might have happened during the Earth's

past. As the particles pile up on the ocean floor, they begin to exert pressure on the

sediments below. What do you think will happen to these sediments over time?

Explain.__________________________________________________________

__________________________________________________________________________

(2.2) Below is a 6 m long core sample taken from the deep sea floor off shows fine grained mud

layers alternating with sandier layers. The volcanic ash at the bottom is dated as 7700 years

old (after Adams, 1990). How many alternating sand-mud layers do you count?

__________________________________________________________________________

(2.3) How can you explain these alternating course, sandier layers with fine particle mud layers?

(HINT: Note that this sample core was taken in a submarine canyon)___________________

___________________________________________________________________________

Oceanography 101 LAB 3 Saunders

(2.4) Given the location of the core sample and its proximity to the Cascadia Subduction Zone,

these alternating sandy-mud silt deposits are probably caused by megathrust earthquakes. A

megathrust earthquake occurs where one tectonic plate is forced under (subducts) another.

Due to the shallow dip of the plate boundary, these earthquakes are among the world's

largest, with moment magnitudes (Mw) that can exceed 9.0. So how many megathrust

earthquakes have we had in this region over the past 7770 years?______________________

3. Hood Canal Bathymetry

INTRODUCTION: If you haven’t heard the news lately, Hood Canal is in trouble. Large inputs

of non-point and point source runoff and have lead to low oxygen environments especially in the

deeper basins of Dabob Bay and Hoodsport. Let’s examine the bathymetry of Hood Canal to see

if it can lend any clues as to why this particular part of Puget Sound is so impacted.

Core sample

site

Oceanography 101 LAB 3 Saunders

(3.1) Obtain a map of Hood Canal. What is the scale on the map?_________________________

(3.2) What unit are the depth measurements?______________

(3.3) Obtain a straight edge and a pencil. Starting out near the opening of Hood Canal (near

Admiralty Inlet) draw a light pencil line down the center of the canal using a straight edge,

changing direction as the canal varies. Continue drawing a center line the entire length of Hood

Canal all the way to Lynch Cove. How many nautical miles long was your line?_________

______________________________________________________________________________

(3.4) If you were to divide your line into 30 increments, how many nautical miles would each

increment be?__________________________________________________________________

(3.5) Estimate the depth at each of the 30 points and fill in the table below. Remember to make

depth numbers negative. Using Excel or other spreadsheet program, plot the bathymetry of

Hood Canal along your line with a 30 increment setting (i.e. divide your line into 30 equal points

and plot each point with the depth in fathoms). Include a print out of the graph with this lab

making sure you have a title, description and properly labeled axes.

Transect Depth in

_____

Transect Depth in

_____

1. 16.

2. 17.

3. 18.

4. 19.

5. 20.

6. 21.

7. 22.

8. 23.

9. 24.

10. 25.

11. 26.

12. 27.

13. 28.

14. 29.

15. 30.

(3.6) Describe the overall shape of Hood Canal’s bathymetry.____________________________

______________________________________________________________________________

(3.7) What is the origin of the Hood Canal Basin (i.e. how did it form?)____________________

______________________________________________________________________________

Oceanography 101 LAB 3 Saunders

(3.8) Are there any features of Hood Canal’s bathymetry that your group can see that might

influence its circulation? Explain.__________________________________________________

______________________________________________________________________________

(3.9) Locate on your bathymetric drawing of Hood Canal a inlet named Dabob Bay. This area

has been in the news recently as a place in trouble because of pollution and nutrient runoff from

the surrounding farmlands and urban areas. Is there anything that you can see from its

bathymetry that might indicate it has a particular susceptibility to these problems? Explain.

______________________________________________________________________________