Water disasters

Floods

A flood is an overflow or accumulation of an expanse of water that submerges land, a deluge. Flooding may result from water within a body of water, such as a river or lake, which overflows, with the result that some of the water escapes its boundaries. While the size of a lake or other body of water will vary with seasonal changes, it is not a significant flood unless water endangers land areas used by man like a village, city or other inhabited area.

There are many effects of floods; the main one being people and livestock die due to drowning. Other effects include contamination of water, unhygenic conditions, shortage of crops and economical conditions, due to lack of tourism, building costs, and food shortage leading to price increase.

In many countries across the world, rivers prone to floods are often carefully managed. Defences such as reservoirs are used to prevent rivers from bursting their banks. When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used. Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls and barrier islands.

There are many disruptive effects of flooding on human settlements and economic activities. However, flooding can bring benefits, such as making soil more fertile and providing nutrients in which it is deficient.

Limnic eruptions

A limnic eruption is where CO2 suddenly erupts from deep lake water, however these eruptions are very rare.

Scientists believe landslides, volcanic activity, or explosions can trigger these eruptions. Lakes in which such activity occurs may be known as limnically active lakes or exploding lakes. Some features of limnically active lakes include:

• CO2-saturated water
  
• A cool lake bottom


• An upper and lower thermal layer with differing CO2 saturations


• Close to areas with volcanic activity

To date, this has been knowingly observed only twice. The first was in Cameroon at Lake Monoun in 1984, causing the death of 37 people living nearby. A second, deadlier eruption happened at neighbouring Lake Nyos in 1986, this time releasing over 80 million cubic meters of CO2 and killing between 1,700 and 1,800 people.

Once an eruption occurs, a large CO2 cloud forms above the lake and expands to the neighbouring region. Because CO2 is denser than air, it has a tendency to sink to the ground while pushing breathable air up. As a result, life forms that need to breathe oxygen suffocate once the CO2 cloud reaches them, as there is no breathable air.

Tsunamis

A tsunami is a series of water waves that is caused when a large volume of a body of water, such as an ocean, is rapidly displaced.

Earthquakes, volcanic eruptions and other underwater explosions, landslides and other mass movements and disturbances above or below water all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating.

There is often no advance warning of an approaching tsunami. If the first part of a tsunami to reach land is a draw back rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami. If people are in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.

Tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia–Pacific region—particularly Japan. The 2004 Indian Ocean Tsunami caused approximately 350,000 deaths and many more injuries.