Massive deadly drain that is world's largest branded 'portal to the middle of the Earth'

Images of the world's largest drain hole, dubbed a "portal to the middle of the Earth", show vast amounts of water swirling down seemingly unendingly into the vast hole in the US.

The man-made hole is called the Morning Glory Spillway and empties water from Lake Berryessa at the Monticello Dam in California to stop flooding.

Built in the 1950s, with a diameter of 22 metres, the dam functions as part of an irrigation system, as the lake provides water for nearby agriculture in the Sacramento Valley.

Images from a drone sent over the hole by YouTuber Matt Casias show the water pouring down 93 metres, as the drain hole works when the water in the dam reaches a high level.

Sadly the drain hole claimed the life of Emily Schwalek in 1997, when she was paddling in the lake and got caught in the current which swept her into the hole.

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Acording to reports of the incident she held onto the rim for about 20 minutes before falling.

Today the hole no longer poses such a risk as the reservoir is roped off and swimming and boating is banned.

Lake Berryessa itself can hold around 52 billion gallons of water before the excess begins to flow into the spillway, with the lake reaching full capacity in 2018 for the first time in 11 years.

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Drone footage of the hole has attracted over one million views online, with the first snaps being posted in 2018 when the drain hole came to more prominence.

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?", while another added: "That right there is the portal to hell."

There is another "door to hell" elsewhere in the world in Turkmenistan, a fiery pit formed after the ground collapsed during a Soviet mining expedition in the 1970s.