Tsunami Initiation

A sudden offset changes the elevation of the ocean and initiates a water wave that travels outward from the region of sea-floor disruption. Tsunamis can travel all the way across the ocean generating destructive waves.

Tsunamis are initiated by a sudden displacement of the ocean, commonly caused by vertical deformation of the ocean floor during earthquakes. Other causes such as deformation by landslides and volcanic processes also generate tsunamis.
The speed of this wave depends on the ocean depth and is typically about as fast as a commercial passenger jet (about 0.2 km/s or 712 km/hr). This is relatively slow compared to seismic waves, so we are often alerted to the dangers of the tsunami by the shaking before the wave arrives. The trouble is that the time to react is not very long in regions close to the earthquake that caused the tsunami.

In deep water tsunamis are not large and pose no danger. They are very broad with horizontal wavelengths of hundreds of kilometers and surface heights much smaller, about one meter.

Tsunamis pose no threat in the deep ocean because they are only a meter or so high in deep water. But as the wave approaches the shore and the water shallows, all the energy that was distributed throughout the ocean depth becomes concentrated in the shallow water and the wave height increases.

When a tsunami approaches the shore, the water depth decreases, the front of the wave slows down, the wave grows dramatically, and surges on land.
Typical heights for large tsunamis are on the order of 10s of meters and a few have approached 90 meters (about 300 feet). These waves are typically more devastating to the coastal region than the shaking of the earthquake that caused the tsunami. Even the more common tsunamis of about 10-20 meters can "wipe clean" coastal communities.
Deadly tsunamis occur about every one to two years and they have at times killed thousands of people. In 1992-93 three large tsunamis occurred: one in Japan, Indonesia, and Nicaragua. All struck at night and devastated the local communities.

Estimating Earthquake

Earthquakes can be estimated by hazard maps, which are constructed by examining

· The earthquake history of the region to estimate the probability of an earthquake
· The expected shaking intensity produced by the earthquake (often expressed as a peak acceleration)
· The frequency of the shaking, the distance from the fault
· The regional geology and site conditions

Hazard mapping is to estimate the maximum level of shaking expected during the lifetime of a building. Constructing accurate hazard maps is a challenge and remains the focus of much Geoscience research.

Climate Change Effects on Plants

Climate change is projected to cause major changes in plant life distribution. For instance giant ferns and marsh plants are forerunners of other kinds of vegetation that developed more recently in Earth's history. As global temperatures increase and other aspects of climate evolve, researchers expect many plant zones to shift away from the equator and toward the poles.

Plants affect climate by absorbing and emitting gases and radiation, so changes in plant distribution due to climate change could produce complex feedbacks that reshape the atmosphere.

Researchers in the National Center for Atmospheric Research's Climate and Global Dynamics Division are addressing a global rise in sea level of 10 to 20 centimeters during the 20th century, probably resulting from the enhanced greenhouse effect, a general warming trend caused by the increase of carbon dioxide and other trace gases in the atmosphere.

The melting of land-based ice sheets and glaciers and the expansion of oceans by warming are factors in sea-level rise. Very large rises in sea level eventually would cause flooding in major coastal cities and large parts of low-lying countries.

Effects of Climate change in South Asia

Asian Development Bank (ADB) warned that more than 1.6 billion people in South Asia, particularly in Afghanistan, Bangladesh, India and Nepal, could face acute water and food shortages from the melting of the Himalayan glaciers as a result of climate change. The retreat of the glacier from the Himalayas would trigger floods, droughts and erratic rainfall that could lead to crop failures.

Analysis of the current trend suggested that by 2050, the climate-induced heat and water-stress would phenomenally lower the yields of irrigated crops – maize (17%), wheat (12%) and rice (10%). The resulting food scarcities will shoot-up food prices and reduce the calorific intake across the region.

Almost half of the world’s absolute poor live in South Asia, where they tend to depend in rain-fed agriculture and live in settlements that are highly exposed to climate variability said ADB. Some of the measures discussed to tackle the problems are agricultural adaptation techniques, investments in irrigation expansion and water resources management, farm-to-market roads, and agriculture research and dissemination to reduce the region’s vulnerability to climate change.

Regional Conference on Climate Change

The statement, agreed during the South-Asian Climate Conference on September 01, 2009 held in Kathmandu, said that South Asia including Hindu-Kush Himalayan region is a climate change hotspot influencing half the world’s population and ecosystems from the mountains to the coast and the seas. All the participating countries (Afghanistan, Bangladesh, India, Maldives, Nepal, Pakistan and Sri-Lanka) agreed that the climate change is affecting the natural resources. The recent effect on water resources is the alarming one. The agreement will call for financing mechanism on adaptation and transfer of technologies from the developed countries to ensure green development during the United Nations Conference at Copenhagen in December.