# Enigma 2 / Depth of Hess Deep Rift : how we know how deep is it ?

Depth of the seefloor

In a few days the ship will operate in the Hess Deep Rift, a deep rift in the Pacific.

How to know how deep is it ?

Scientists use sound waves. The principle is simple, it is the echo. A sound pulse is emitted from the ship towards the bottom, where it is reflected and returns to the surface: scientists record its echo, and measure the travel time to go back.

It reminds me of the storm: We can evaluate the distance of the storm by counting the number of seconds between the vision of lightning and thunder, and multiplying this number by 300 (speed of sound = 300 m/s), we have the distance separating us from the storm in meters. We can hear ‘the storm is at 7 seconds’ to be translated by ‘the storm is located three km far from usâ€™ (300 x 7 = 2 100 m).

The researchers recorded a time of 7 seconds in Hess Deep Rift * to the path of the waves in the water.

What the scientists will conclude:

1 : The depth of the rift is 2Â 100 m
2Â Â Â  : The depth of the rift is 1 050 m
3 : The depth of the rift is 5Â 250 m

Answer to this enigma by a comment !

Solution next sunday … on the blog