Page 249 - The British Big Four

lue holes are typically found on shallow white carbonate sand. Blue light is the he formation process consists of three

B carbonate platforms, exemplified by the most enduring part of the spectrum; other T phases, dissolution, collapse and con-
Bahama Banks, as well as on and around the parts of the spectrum—red, yellow, and fi-
struction. Blue holes are formed by disso-
Yucatán Peninsula, such as at the Great Blue nally green—are absorbed during their path lution of rock and the resulting subsurface
void, which may or may not be linked to
Hole at Lighthouse Reef Atoll, Belize. Many through water, blue light manages to reach an active cave system, and the subsequent
structural collapse of the rock ceiling above
deep spring basins formed by karst process- the white sand and return upon reflection. the void. Rock that falls into the water below
is slowly removed by further dissolution,
es and located inland also are called blue creating space for more collapse blocks. The
holes, for example, Blue Hole (Castalia) in rate of collapse increases during periods
lue holes have a very similar formation pro- when the water table is below the ceiling of
BOhio. Blue holes are roughly circular, steep- cess to Centoes. Blue holes formed during the void, since the rock ceiling is no longer
buoyantly supported by the water in the
walled depressions, and so named for the past ice ages, when sea level was as much void. Cenotes may fully collapse creating an
open water pool, or partially collapsed with
dramatic contrast between the dark blue, as 100–120 metres (330–390 ft) lower than some portion of a rock overhanging above
the water.
deep waters of their depths and the light- at present. At those times, these forma-

er blue of the shallows around them. Their tions were targets of the same erosion from

water circulation is poor, and they are com- rain and chemical weathering common in

monly anoxic below a certain depth; this en- all limestone-rich terrains; this ended once

vironment is unfavorable for most sea life, they were submerged at the end of the ice

but nonetheless can support large numbers age.

of bacteria. The deep blue color is caused by

the high transparency of water and bright