Marie Tharp was an American oceanographic cartographer and geologist who, along with Bruce Heezen, created the first scientific map of the entire ocean floor. Tharp's work revealed the existence of the Mid-Atlantic Ridge and revolutionized the scientific understanding of continental drift.

How did she do it? Imagine...

A research vessel leaves the coast of Peru, near Lima, and travels 3,600 km to the west. As you go, your echosonar continuously records the depth of the ocean floor below sea level. Some of the echosonar readings are shown in the table.

1.- Calculate the missing depths in the table

Distance from Lima (km) Time to go and return Depth (m)
0 (to the port) 0,02 15
100 0,27  
200 1,60 1197
300 10,69  
400 7,06 5299
500 6,66 4998
600 6,64 4977
700 6,60 4949
800 6,54 4907
900 6,52 4900
1000 6,50  
1100 6,49  
1200 6,43 4823
1300 6,43 4823
1400 6,40 4802
1500 6,34 4753
1600 6,29 4718
1700 6,26  
1800 2,67  
1900 6,20  
2000 6,16 4620
2100 6,13 4599
2200 6,07 4550
2300 5,94 4452
2400 5,87 4403
2500 5,60 4200
2600 5,07 3801
2700 4,80 3598
2800 4,27 3199
2900 4,00 3003
3000 3,73  
3100 3,42 2562
3200 2,80 2100
3300 2,67  
3400 4,67  
3500 2,67  
3600 3,33 2499

 

2.- Draw a graph of all the depths from the coast of Peru to the west of this part of the Pacific Ocean.

3.- Colour the graph: Continental Shelf – depth less than 150 m; continental slope – depth from 150 m to 2000 m; Peru/Chile Trench – depth of 8000 m; abyssal plain – very flat seabed at about 5,000 m depth; seamount – isolated underwater peak that rises to 2000 m or less below sea level; East Pacific Ridge – a submarine ridge about 2,000 m deep; rift valley of the Eastern Pacific ridge – about 3500 m deep.

4.- Explain, according to the theory of plate tectonics, the origin of:

a) The Peru/Chile Trench.

b) The East Pacific Ridge.

c) The rift valley along the middle of the East Pacific ridge.

d) The seamount.