While the park has added newer amusements, most visitors come for the vintage attractions, including a two-tier carousel built in 1921, the Talaia, which raises guests with a rickety metal arm to a height of 550m above sea level, and the iconic Avio ride, modelled on the first plane to fly between Barcelona and Madrid.

BBC: Europe��s grand old theme parks

The time taken for the waves to complete this journey is recorded, and it is a fairly straightforward calculation to work out the height of the ice above sea level.

BBC: Arctic ice thickness 'plummets'

The levees intended to protect the city vary in height, from as low as 10 feet above sea level to about 14 feet, he said.

CNN: Expert: Katrina could unleash disaster

In two weeks' time, murky brown water will have backed up behind the dam to a height of 135 metres (440 feet) above sea-level.

ECONOMIST: A river is blocked, but criticism continues to flow