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Just one knock is all it takes
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Secrets of the Underground

Just one knock is all it takes to tell us there's an abrupt densitychange behind this wall

Just one knock is all it takes to tell us there's an abrupt density
change behind this wall

Full Transcript

00:00:01.000 --> 00:00:02.092
Just one knock is all it takes
00:00:03.000 --> 00:00:06.032
to tell us there's an abrupt density change behind this wall.
Duration
6 seconds
Views
13
Timestamp in Movie
00:18:28
Uploaded
Jul 09, 2025
Season
1
Episode
2
Genres
documentary

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Movie Summary

Using cutting-edge technologies such as ground penetrating radar (GPR), LIDAR (Light Detection and Ranging), and 3-D imaging, scientists research fascinating underworlds of secret tunnel networks, ancient structures, and bizarre g...
S01 • E07 Well, from what I know About volcanos, - Secrets of the Underground 00:06
Well, from what I know About volcanos,
S01 • E01 This section of this room very well could have been the stairway. - Secrets of the Underground 00:05
This section of this room very well could have been the stai...
S01 • E08 Before Alcatraz was a federal penitentiary, - Secrets of the Underground 00:07
Before Alcatraz was a federal penitentiary,
S01 • E02 Maybe let's go further down - Secrets of the Underground 00:05
Maybe let's go further down
S01 • E07 This could be a frightening sign That trouble is brewing. - Secrets of the Underground 00:04
This could be a frightening sign That trouble is brewing.
S01 • E08 He tells me that these fortifications were built around 1860, - Secrets of the Underground 00:07
He tells me that these fortifications were built around 1860...
S01 • E07 Have often preceded Devastating eruptions. - Secrets of the Underground 00:04
Have often preceded Devastating eruptions.
S01 • E03 The thinking is, "Go after the intruders." - Secrets of the Underground 00:10
The thinking is, "Go after the intruders."
S01 • E07 The largest volcano on earth, Hawaii's mauna loa, - Secrets of the Underground 00:09
The largest volcano on earth, Hawaii's mauna loa,
S01 • E08 So, this is Alcatraz as it is today. - Secrets of the Underground 00:04
So, this is Alcatraz as it is today.
S01 • E01 We have to figure out what's below this. Mh-hm. - Secrets of the Underground 00:05
We have to figure out what's below this. Mh-hm.
S01 • E02 If I was testing a wall in a building, - Secrets of the Underground 00:05
If I was testing a wall in a building,
S01 • E08 Peter has been using old surveying data - Secrets of the Underground 00:07
Peter has been using old surveying data
S01 • E03 You suddenly get sick, so why not blame it, basically, - Secrets of the Underground 00:06
You suddenly get sick, so why not blame it, basically,
S01 • E07 Understanding these changes Helped volcanologists predict. - Secrets of the Underground 00:04
Understanding these changes Helped volcanologists predict.
S01 • E01 Now I want to trace this shaft down into the basement, - Secrets of the Underground 00:09
Now I want to trace this shaft down into the basement,
S01 • E07 Massive eruptions In 1975 and 1984. - Secrets of the Underground 00:06
Massive eruptions In 1975 and 1984.
S01 • E02 We gotta go downtown and see if we can find the tunnels there. There is definitely a connection. - Secrets of the Underground 00:06
We gotta go downtown and see if we can find the tunnels ther...
S01 • E03 An axe wound is an intense wound. Yeah. Yeah, super-violent crimes. - Secrets of the Underground 00:06
An axe wound is an intense wound. Yeah. Yeah, super-violent ...
S01 • E08 Meaning we can move not just through space, but through time. - Secrets of the Underground 00:05
Meaning we can move not just through space, but through time...