Measuring the depth of seas and oceans: How is it done?
Personajes:
Tema: Plate tectonics
Competencias
Competencia Matemática, en ciencia, tecnología e ingeniería
Competencia Ciudadana
Materias y cursos por Sistema Educativo
España > Biología y Geología > 4º ESO > Geología
Enunciado
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.
Observaciones y contexto
In 1940, the geology department of the University of Michigan in the USA allowed women to access the department for the first time. Marie Tharp was one of the first women to enter, graduating in 1945. At the same time, Rosalind Franklin, the chemist who would later be one of the discoverers of DNA, was attending classes at Cambridge University and passing exams with flying colours, but she was unable to graduate or take part in the graduation ceremony because she was a woman. These examples show the difficult world in which women scientists had to work in at the time.
Descripción
Students can:
• calculate ocean depth from the round trip time of sound waves
• draw a graph of depths across the Pacific Ocean
• describe the characteristics of their depth profile
• relate this profile to the plate tectonics theory
Echosonars were first used in the 1920s to measure the depth of the sea and to detect other ships or obstacles. They send a sound wave to the bottom of the sea and count the time it takes for the “ping” to return. This time can be used to calculate the depth if the speed of sound in water is known.
The speed of sound in seawater varies between 1450 ms-1 and 1570 ms-1, depending on salinity, temperature and pressure, but we use 1500 ms-1 for the calculations.
Remember that "t" is the time it takes for the wave to travel to and from the ocean floor. We will have to divide by 2 to calculate the depth of the ocean.
Speed (s) = Distance(d) / Time (t)
Thus the Distance (Depth) = s·t
But remember that "t" is the time it takes for the wave to go to the ocean floor and return, so we have to divide the value by 2.
Sea depth (d) = s·t / 2
This activity is a summary of the activities proposed in:
https://www.earthlearningidea.com/Indices/contents_Spanish.html
https://www.earthlearningidea.com/PDF/352_Spanish.pdf
Very interesting and simple!