Earth's Structure

In a previous post of mine named Onion Earth I explained how the earth has a layered structure somewhat resembling an onion. The earth has several layers such as crust, mantle core, asthenosphere, mesosphere etc. Some of these layers overlap each other and thus can create confusion. This problem could be avoided by classifying these layers in two ways, one based on the Chemical composition and the other based on the physical properties.

Based on Chemical composition, three layers are identified.
1. Crust  -  Abundant in elements Si , O, Al, Mg, and Fe
2. Mantle  -  Mainly Fe, Mg, Si
3. Core  -  Ni and Fe alloy

Based on the physical properties five layers are identified.
1. Lithosphere  -  Rigid outer shell. Comprises of the crust and uppermost mantle
2. Asthenoshpere  -  Shows plastic behavior. Lithosphere "floats" on this layer. 5% of rocks in this layer is molten
3. Mesosphere  -  Extends from about 300km to 2000km beneath the surface. Solid
4. Outer Core  -  Molten. Rotates around the inner core and produces the earths magnetic field
5. Inner Core  -  Extreme pressure causes it to stay solid despite the high temperatures

Source : http://www.tulane.edu/~sanelson/images/earthint.gif

Seafood Bliss - Sea Fish Restaurant

Sea Fish is a restaurant dedicated to serving good seafood dishes. Its location behind the Regal cinema in a secluded corner in the Colombo city it helps to maintain the calm and quiet ambience of a good restaurant. They serve a wide selection of seafood main courses out of which my favourite is "Cheese Batter Prawns". They also have some decent Crab dishes as well. The quality of the food and service is considerably better than some other restaurants claiming to serve seafood. It is definitely worth the sea food lovers attention.

A Classification of Ocean Waves

The sight of waves breaking at a shore is common sight to most of us. While it is relaxing to watch the constant pounding of the waves while listening to the hum of the sea, we don't give much thought to the way these waves are formed or the types of waves in the ocean.
Ocean waves are classified into seven major groups depending on their size, period and way of formation. These types are described below.

1. Capillary Waves
Capillary waves are the smallest of these types, having a period generally less than 0.1sec and a wavelength less than a couple of centimeters. Capillary waves are caused by local winds, more specifically short bursts of winds. Capillary waves are similar to ripples created on a body of water by dropping an object into it. The restoring force in the case of capillary waves is surface tension

2. Chop waves
These are the the common waves in the ocean familiar to everyone. These waves have periods of several seconds, and wavelengths ranging from 1 to 10 metres. Chops are wind generated waves. A consistent blowing of find over a considerable fetch(sea surface area over which the wind blows) causes these waves. The restoring force of these waves is gravity.

3. Swells
Swells are much larger wind generated waves. Very powerful winds are required for the creation of these waves and they are related to distant storm surges. Periods can vary between 10 and 30 seconds and wavelengths are in the order of hundreds of metres. Swells occurring alongside a storm in coastal ares can have devastating effects.

4. Seiches
Seiches are standing waves that can be created by wind, seismic disturbances or by tidal resonance. The word seiche originates in a Swiss French dialect word that means "to sway back and forth". This an accurate description of the wave because it actually sways to and fro like a see-saw. These waves can be generated at harbours, estuaries, lagoons and even swimming pools. You can visualize a seiche by giving a nudge to your tea cup. The resulting oscillatory motion of the liquid in the cup is similar to that of a seiche. Seiches can have periods ranging from a couple of minutes to several hours and wavelengths upto hundreds of kilometres.

5. Tsunamis
Tsunamis are massive and catastrophic waves generated by submarine disturbances. Two major tsunamis have occurred during the past decade causing severe destruction to places affected. The most common submarine activity leading to tsunamis is subduction between tectonic plates. However other disturbances such as landslides could also produce tsunamis. Tsunamis can have a period of about an hour and wavelength can reach hundreds of kilometres.

6. Tides
Tides that are caused by the gravitational attraction of the sun and moon are familiar to us but few realize that it is classified as a wave. Tides have periods of 12.8 or 24.8 hours and are related to the earths speed of rotation. Wavelengths are in the order of thousands of kilometres.