Phys.org's story from September 23, 2022 entitled Mexico earthquake triggers 'desert tsunami' 1,500 miles away in Death Valley cave includes the following:
About five minutes after the 7.6 magnitude earthquake hit near Mexico's southwest coast Monday, typically calm water deep in a Death Valley National Park cave started sloshing against the surrounding limestone rock.
The reverberations from the earthquake more than 1,500 miles away created what experts have called a "desert tsunami," which on Monday made waves erupt up to 4 feet high in the cave known as Devils Hole, a pool of water about 10 feet wide, 70 feet long and more than 500 feet deep, in Amargosa Valley, Nevada.
The water in the partially filled cave has become an "unusual indicator of seismic activity" across the world, with earthquakes across the globe—as far as Japan, Indonesia and Chile—causing the water to splash up Devils Hole, according to the National Park Service website.
"It depends on the depth, magnitude and location around the world," Wilson said. He said typically earthquakes along the Pacific's "Ring of Fire" that reach at or above a magnitude 7 will register in Devils Hole.
Question: How did they know that there was a "desert tsunami" in a Death Valley cave after a 7.6 magnitude earthquake near the southwest of Mexico?
I'm wondering if there are video cameras inside, or water height sensors that record wave height, or was there just a puddle of water outside the opening in the morning?
Since the article begins "About five minutes after the 7.6 magnitude earthquake hit..." it suggests there were some type of live data collected, although that could simply be an estimate somehow?