Page 24 - How It Works - Book Of Amazing Answers To Curious Questions, Volume 05-15

What are sinkholes?

The rare phenomenon behind
that sinking feeling
inkholes form when water slowly erodes the
S bedrock underground, until the surface is no
longer supported and collapses into the cavity
beneath. This occurs most commonly in areas where
the bedrock is made from salt or carbonate rocks
(such as gypsum or limestone), which are particularly
susceptible to dissolving.
In the absence of surface drainage, water
accumulates in the sinkhole, draining through to the
subsurface. Cover-subsidence sinkholes create a
small depression at the surface, which sinks slowly.
Cover-collapse sinkholes are far more dramatic,
collapsing in a matter of just a few hours and
potentially causing catastrophic damage. One of the
most spectacular sinkholes ever seen opened up in
Guatemala City in 2010, swallowing a three-storey
building. It measured 20 metres (66 feet) across and
had a depth of 30 metres (98 feet). Sinkholes are a
natural phenomenon, but manmade changes to
drainage flows (such as ground pumping) or land use
changes can encourage them to occur.

Why do lizards like to

bask in the sun?

What’s behind the sun-seeking behaviour
of these sneaky amphibians?
izards are covered with scales, which are very good at preventing
L moisture loss, but pretty bad at keeping in body heat. Because of
this, lizards and other reptiles don’t try to maintain such a fixed internal
body temperature as birds and mammals do. At night their body
temperature drops, so in the morning they bask on a rock until the Sun
has warmed them up enough for their metabolism to operate efficiently.
This strategy restricts most reptiles to warmer countries, but it also allows
them to get by with much less food than mammals. For example, some
crocodiles can go for a year without eating.

24 How It Works