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This cave IS a natural formation.

Not like those other FAKE caves!

Yeah.

#dougie rambles #personal stuff #caves #geology #my poor attempt at a joke #this sounded funnier in my head #halo #bungie #343 industries #halo studios

Measuring the Earth's tides with the world's largest geodetic pendulum

Deep in Italy's largest cave, you'll find Italy's largest pair of pendulums. The Grotta Gigante, which creatively means "Giant Cave" is an enormous cavern in northeastern Italy near the border with Slovenia. The main hall is 351 feet high and 430 feet wide. In addition to making it a beautiful tourist attraction, it's home to a rather important and colossal scientific instrument.

Earth tides are something I've mentioned before: The Sun and Moon have an obvious effect on the height of the sea in the form of oceanic tides, but they also stretch and squeeze the land itself. The crust of the Earth is only an average of 22 miles thick, and it's moved up and down by these tidal forces about ten centimeters per day.

In addition to this, the crust is also moved by tectonic forces, which most often you see as earthquakes. After that, you have the ocean tides making an impact too: All that water moving about weighs the earth down and shifts it.

How do you measure these effects? Why, a pendulum, of course! Were it not for these outside impacts, a pendulum should move stably. So with a large enough pendulum to detect the changes in the crust, you can determine what's actually happening.

The next trick is that you also need to avoid interference, such as heavy traffic nearby. The Grotta Gigante turns out to be the perfect location to install a pendulum, and so one was built in 1959. It's a horizontal pendulum, so there's a steel beam weighing about 18,000 kilograms suspended by wires running to the top and bottom of the cavern.

From there, a small mirror is mounted on the beam, and a light aimed at it and reflected onto a sensor can pick up the most minute of movements. So really, what it is is a massive tiltmeter.

The Grotta Gigante horizontal pendulums are an incredibly valuable scientific tool. You can determine the Earth tides by looking for periodic movements, and outliers will be seismic activity. The pendulums have recorded four of the five most powerful earthquakes of the last half-century, including two in Chile. There's a lot of value in having the same instrument measure different events.

As for superlatives... Wikipedia denotes it as the "world's largest geodetic pendulum", but when I looked up the term, I could only find the Grotta Gigante pendulums anyways. So sure, they can have it.

#geology #science #caves #earth science #speleology #physics