The strange phenomenon took place in the Lake Berryessa reservoir in the eastern Napa Valley. If water levels in the reservoir, which lies at the top of the Monticello Dam, get too high, excess water can whirlpool into a gigantic hole. A 22-metre-wide (72 ft), 75-metre-long tunnel which functions as a drain hole (245 ft) swallowing around 1,360 cubic metres of water (48,000 cubic feet) per second when the lake rises above 4.7 metres) 15.5.
This is what creates the spectacular spinning vortex effect.
It has once again been spotted on the surface of the lake.
Locals have caught sight of this on various occasions and have dubbed the event the ‘Glory Hole’.
A spillway was deliberately built by engineers back in the 1950s as an alternative to the more common chute.
This is used to control the flow of water out of a dam or a levee.
The artilects decided to construct the drain-like feature in the dam as the narrow gap between cliffs where the dam is situated would have left the chute with nowhere to go.
And now, the “Glory Hole” has garnered itself quite the reputation.
In 2017, it drew hundreds of spectators who came to watch the fascinating spectacle of the “portal” opening up.
Lake Berryessa can hold around a 52 1billion gallons of water before the excess begins to flow into the spillway.
It reached its full capacity for the first time in 11 years back in 2018.
It also opened up again in 2019 after a season of heavy rainfall, reportedly attracting thousands of baffled onlookers.
One comment read: “Why is there a giant hole in the middle of the lake where people swim, and why is there not a rope around?”
Another added: “That looks very unsafe.”
And a third stated: “That right there is the portal to Hell.”
Similar to the “portal from hell” in California, a fiery pit in Kazakhstan earnt itself a similar nickname.
Officially named the Darvaza Crater, the fiery pit was formed back in the early 1970s when the ground collapsed during a Soviet gas drilling expedition.
The hole is 20 metres deep and 60 metres (190ft) wide. It is located in the Karakum Desert, about 160 miles north of capital city Ashgabat.
Scientists are said to have lit the giant hole on fire to prevent the spread of natural gas, and the fire has kept burning ever since.