Quezi

The Seven Sisters cliffs with Belle Tout lighthouse in the distance (photo by clagnut CC-BY)

Fortunately there are three examples from Britain and the US that provide the answer. Each presented their own special set of problems.

Belle Tout Lighthouse on the Sussex coast in England is perched on the edge of the famous Beach Head chalk cliffs which are rapidly eroding. Built in 1835 some 34 metres from the edge of the cliff, it was decommissioned in 1902. By 1999 the lighthouse was perilously close to the edge, to such an extent that within one winter the cliff could crack and tumble into the sea taking the lighthouse with it. What made it more dangerous was that the lighthouse was somebody’s home.

Funds were raised by the owner of the lighthouse and local people, and on 19 March 1999 the 850 tonne lighthouse was moved.

The move was complicated by the fact that the ground on the safe side of the lighthouse fell rapidly away down a hill and the chalk was very soft and crumbly. First, preliminary work required the ground around the building to be excavated, but no heavy plant could be used so excavation was by wheelbarrow. Also prepared was a new basement onto which the lighthouse was to be placed.

On the day of the move, 30 hydraulic jacks raised the lighthouse, sliding tracks were installed, it was then lowered onto greased skates. The entire building was then very slowly pulled away from the cliff edge. Over the next two days it moved 17 metres to its new position.

Although now moved, it is still very close to the edge as can be seen in the photograph.

If you are interested in a more technical explanation then visit Cranes Today Magazine

In 1999, the lighthouse at Cape Hatteras, North Carolina, was only 120 feet from the ocean and erosion threatened to collapse it. Built 1868-70, the lighthouse is approximately 208 feet tall and weighing about 4,400 tons. It presented a different engineering challenge to that of the Belle Tout.

The engineers first had to remove 800 tons of the granite base, replacing it with steel support towers, then using hydraulic jacks the lighthouse was lifted up and steel support beams installed. It was then transferred to a support steel frame which allowed the lighthouse to move easily and kept level. It then was moved on a prepared roadway, over a period of 23 days, 2,870 feet inland to its new location.

If you are interested in a more technical explanation then visit U.S. Department of the Interior National Park Service.

Another example is the Southeast Lighthouse on Block Island, Rhode Island in 1993.