The blue hole

This incredible geographical phenomenon known as 'the blue hole' is situated 60 miles off the mainland of Belize . There are numerous blue holes around the world, but none as stunning as this one.

A feature attraction of Diving in Belize, Especially for divers with a appreciation of geographical phenomena, is the opportunity to explore the famed Blue Hole. Part of the Lighthouse Reef System, it lies approximately 60 miles off the mainland out of Belize City. It is one of the most astounding dive sites to be found anywhere on earth, right in the center of Lighthouse Reef is a large, almost perfectly circular hole approximately one quarter of a mile (.4 km) across. Inside this hole the water is 480 feet (145 m) deep and it is the depth of water which gives the deep blue color that causes such structures throughout the world to be known as "blue holes."

Like a giant pupil in a sea of turquoise, The Blue Hole is a perfectly circular limestone sinkhole more than 300 feet across and 412 feet deep. The array of bizarre stalactites and limestone formations which mould its walls seem to become more intricate and intense the deeper one dives. Near to The Blue Hole, one of Belize's largest protected areas, Half Moon Caye Natural Monument, encompasses 10,000 acres of the atoll and 15 square miles of surrounding waters.

The diameter of the circular reef area stretches for about 1,000 feet and provides an ideal habitat for corals to attach and flourish. The coral actually breaks the surface in many sections at low tide. Except for two narrow channels, the reef surrounds the hole. The hole itself is the opening to a system of caves and passageway that penetrate this undersea mountain. In various places, massive limestone stalactites hang down from what was once the ceiling of air-filled caves before the end of the last Ice Age. When the ice melted the sea level rose, flooding the caves.

The temperature in the Blue Hole at 130ft is about 76F with hardly any change throughout the year at that depth.

For all the practical purposes the over 400-foot depth makes the Blue Hole a bottomless pit. The walls are sheer from the surface until a depth of approximately 110 feet where you will begin to encounter stalactite formtions which actually angle back, allowing you to dive underneath monstrous overhangs. Hovering amongst the stalactites, you can't help but feel humbled by the knowledge that the massive formation before you once stood high and dry above the surface of the sea eons ago. The feeling is enhanced by the dizzying effect of nitrogen breathed at depths. The water is motionless and the visibility often approaches 200 feet as you break a very noticeable thermocline. 

Meanwhile, something altogether different and Jules Vernian is about to occur thanks to some Japanese scientists hoping to drill down into the earth’s mantle: “Using a giant drill ship launched [in July 2005], the researchers aim to be the first to punch a hole through the rocky crust that covers our planet and to reach the mantle below.”
And then, in an oddly Borgesian, or perhaps MC Escherian, moment of nomenclatural mise-en-abîme, “The 57,500-tonne drill ship Chikyu (Japanese for Earth) is being prepared in the southern port of Nagasaki. Two-thirds the length of the Titanic, it is fitted with technology borrowed from the oil industry that will allow it to bore through 7,000 metres of crust below the seabed while floating in 2,500 metres of water – requiring a drill pipe 25 times the height of the Empire State building.”
For some sense of perspective here, the diamond mine, pictured above, is 1200 meters deep; that means that to reach the mantle, the Japanese will have to produce a drill-hole nearly seven times deeper than the mine (which sounds alarmingly easy, actually – I was expecting to be horrified).
In any case, the drill-ship is called *Earth* and it’s being drilled down into the earth… The attack of the simulacra begins.

[Note: This post originally stated that the mine was in South Africa – but I've corrected myself thanks to the comment, below. And apologize. It is, in fact, in Russia as this BBC slideshow – which I actually looked at a few days ago without noticing (uh...) – makes clear. This BBC link also inverts the figures I had, so who knows: I had 1200m deep and 500m wide (which I suppose is a bit unlikely); the Beeb says the opposite. If that is the case, however, then that Japanese bore-hole into the earth's mantle will actually be at least *fourteen times* deeper than the Mirny mine...]