Just Let That Sink In Trivia Quiz

Answer: Skyscrapers

A feature of being on a river delta is the soft soil. Combine this with a population rising from a million in 1900 to over 23 million by 2010 and you can imagine a few environmental pressures. Over-extraction of groundwater resources has been recognised as a problem for some time however this has been partially addressed by pumping water back into the ground - around 60,000 cubic metres daily according to one source.

A perhaps unexpected problem has been the building of skyscrapers. As the population has increased so has the demand for land. This results in buildings going upwards. In 2011 alone some 200 skyscrapers were built in Shanghai and many more are anticipated. Skyscrapers impose a large load on a relatively small surface area which, with soft soil acting a bit like a sponge, contributes to localised sinking of parts of the city. Nowadays only a flood wall prevents parts of the city being inundated at high tide or during rainy season.

The photo shows the Pudong area of Shanghai. The Jin Mao Tower (on the right with a needle) used to be the tallest in China at 421 metres. The Shanghai World Financial Center (to the right with the hole in it) topped that at 492 metres however this has been overtaken by the Shanghai Tower (on its right) at 632 metres.

This sort of problem is faced by many cities around the world. Jakarta, capital of Indonesia, is an other example, sinking around ten centimetres per year and has around 40% of its land below sea level.

Answer: Earthquake

It was an earthquake, occurring on June 7 1692 (at 11.43 in the morning according to one watch found in 1969), which proved to be the agent of destruction. The earthquake caused liquefaction which resulted in most of the city disappearing under the waves. During liquefaction, water-saturated soil (in this case sand) behaves like a liquid. The houses, many built of brick on a foundation of sand, appeared to subside into the sea. The tsunami which followed helped to contribute to the destruction.

In all, around 2,000 died during the first day. Another 3,000 or so died in the following days from their injuries or disease, out of a total population of 6,500. There was also much damage and loss of life in other parts of Jamaica. The town was partially-rebuilt but suffered damage over the years from hurricanes, fire and another destructive earthquake in 1907, gradually losing its status to Kingston.

According to the text on the photo, the darker shaded area on the map shows what remained above sea level after the 1692 earthquake.

Answer: An oil rig drilling into the salt mine

A Texaco oil rig accidentally drilled into the salt mine nearly 400 metres below the lake with a 36 centimetre (14 inch) drill bit. Water rushing through the hole quickly dissolved the salt, widening the hole. The whirlpool thus created sucked two drill rigs, eleven barges, a tug, and trees and soil from the surrounding 65 acres into the mine. When the lake level dropped enough, the flow of the Delcambre Canal was reversed and created a temporary 50 metre high waterfall, Louisiana's largest, until the mine was filled some two days later. The tug and barges came from the canal.

No lives were lost. All 55 men working in the mine managed to escape. Nine of the barges popped back to the surface once the mine had filled up. The canal was effectively dredged around a metre deeper by the strength of the water flow. You can now catch salt water fish in the lake, which features an unusual deep section.

The photo shows Delcambre Canal at Delcambre, close to Lake Peigneur. The structure is part of a lifting bridge.

Answer: Sink-hole

A sink-hole is also known as a swallow hole, shakehole, swallet or doline. There are various localised names such as tiankeng and tomo, which are natural sink-holes found respectively in China and New Zealand.

The photo shows Guatemala City and one of the four nearby volcanoes. The city is built on the ash deposited from these volcanoes. These sink-holes were partly caused by leaking sewage pipes eroding away the underlying layers of ash and other volcanic deposits to create a void. Heavy rain events did the rest.

Sink-holes are normally naturally-occurring features formed with the collapse of the surface after the dissolution of the underlying soluble rock, such as limestone. Artificial ones, such as the Guatemala City ones, have been termed "piping pseudokarsts".

Answer: A North Sea storm tide

The Grote Mandrenke (meaning Great Drowning of Men) was caused by a massive south-westerly gale, resulting in the loss of numerous coastal towns and villages and at least 25,000 lives. Storm tides were a feature of the unsettled weather occurring at the start of the Little Ice Age. Such storm tides have changed the shape of the coast around the North Sea.

Another storm tide in 1634, called the Burchardi flood or the Second Grote Mandrenke, destroyed the island itself, breaching dikes and taking up to another 15,000 lives.

The photo is of a shrimp boat with the name of Rungholt. This one was afloat at the time.

Answer: Forestry

During the 18th century, logging became a major industry in the area. The local river, the Indalsälven, and the lake were used to transport the logs to coastal sawmills however the waterfall damaged most of them. Locals were employed to transport the logs by land around the waterfall and so were not keen on the canal. Despite some sabotage, the canal was nearly finished when the accident occurred.

The route chosen was the pre-glacial channel which became choked with unconsolidated glacial debris at some point during the last ice age. Problems with collapsing walls whilst digging out the canal should have been a clue. This however encouraged the use of another technique - damming a stream and releasing it to carve out sections of the channel.

When the lake emptied, the waterfall dried up and was renamed Döda Fallet, which means "dead waterfall" in Swedish. It is now a nature reserve and one of the tourist features of the area. The river never did become navigable, however, on the plus side, the dried lake bed provided new farmland, a new waterfall formed by a rock barrier in the bottom of the former lake enabled a hydroelectric power station to be built, and the debris from the purging created new land on the coast which now has an airport on it.

Answer: Increased glacial melts

Recent monsoons have been more erratic leading to shorter but heavier falls. This does cause flooding and erosion, but no greater than is perhaps normal. What is unusual is the higher glacier melt leading to disappearing glaciers and unseasonally high river flows. The river erosion resulting (see photo) is now more all year around rather than seasonal. It is not all one way. The higher amounts of sediment carried by the rivers lead to new islands forming, however these take time to settle before becoming habitable.

How do higher water temperatures affect the islands? The theory is that this expands the volume of water in the Bay of Bengal, leading to higher tides.

Bangladesh is one of the world's most densely populated countries as well as lowest-lying. Most of the country is less than 12 metres above sea level. It is considered one of the countries most vulnerable to climate change with millions of potential refugees.

Answer: Money Pit

The sink connection here is the money spent on fruitless treasure hunts in what appears to be (according to one theory) a natural sink-hole filled with debris.

It all started with a story about lights seen on the island one night by an 18-year old in 1795. On later investigation, a circular depression was found in a clearing and a block and tackle on an overhanging tree. With some friends, he dug down to uncover a layer of flagstones and then several layers of logs at spaced intervals but gave up 30 feet down. The story was reported and others became interested. A stone with symbols inscribed was found. The symbols were deciphered by someone as meaning that two million pounds lay buried forty feet below.

Over the years various companies have been formed and many spent all their money carrying out excavations, with cave-ins, floodings and accidents accounting for six lives. Franklin D Roosevelt, later to be President of the USA, was involved in one such company, the Old Gold Salvage group of 1909. As for the source of the treasure, many theories abound. Pirate treasure, naval treasure, Marie Antoinette's jewels ...take your pick. It is still to be found.

Another theory is that it is simply a sink-hole connected to natural caverns with trees blown or washed into the hole periodically. Numerous sink-holes together with natural caverns exist nearby on mainland Nova Scotia. In 1949 when digging a well, a similar pit was found also in Mahone Bay, complete with a layer of field stone and irregular layers of spruce and oak.

Answer: Dutch soldiers destroyed the last dike

Strangely enough, it was the Dutch soldiers who did it. During the Eighty Years' War (also known as the Dutch War of Independence), the Dutch soldiers got into a position where they felt that they had no choice but to destroy the remaining dike. The town was abandoned first. Several attempts since to recover the land have been unsuccessful.

There is a Dutch legend to go with the sinking of the town. This involves a curse placed on the town by a merman when a fisherman refused to release his mermaid wife.

The photo shows some of the 19 windmills at Kinderdijk, part of UNESCO World Heritage Site and built around 1740 for drainage purposes.

Answer: Draining the surrounding swamps

Development of New Orleans was constrained by the surrounding swamps so in the early 20th century large tracts of swamp land were drained to allow the city to expand. What was not anticipated was that this land would shrink and subside. Three elements contributed to this: the soil dried out and oxidised, leading to a reduction in soil volume; the draining of the cypress swamps prevented the natural replenishment of the organic matter, and the levées prevented the flooding which would otherwise supply alluvial deposits.

Roughly half of the city removes drainage water by pumping it over the levées. Meanwhile the city continues to sink. The photo shows what can happen when levées and pumps fail.