Types of Rocks Rocks are not all the same! The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed. Sedimentary Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils. Examples of this rock type include conglomerate and limestone. Metamorphic Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface. Examples of this rock type include gneiss and marble. Igneous Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock. Examples of this rock type include basalt and obsidian.

The Earth Profile

THE EARTH PROFILE

 

 

THERE ARE FOUR MAIN LAYERS THAT MAKE UP THE EARTH: 

 

1. Inner Core - A mass of iron with a temperature of about 7000 degrees F. Although such temperatures would normally melt iron, immense pressure on it keeps it in a solid form. The inner core is approximately 1,500 miles in diameter.

2. Outer Core - A mass of molten iron about 1,425 miles deep that surrounds the solid inner core. Electrical currents generated from this area produce the earth's magnetic field.

3. Mantle - A rock layer about 1,750 miles thick that reaches about half the distance to the centre of the earth. Parts of this layer become hot enough to liquify and become slow moving molten rock or magma.

4. Crust - A layer from 4-25 miles thick consisting of sand and rock.

The core, mantle and crust of the earth can be envisioned as a giant rock recycling machine. However, the elements that make up rocks are never created or destroyed although they can be redistributed, transforming one rock type to another.

Tornadoes

Tornadoes

What is a tornado?

A tornado is a violent rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction with wind speeds of up to 300 mph. They can destroy large buildings, uproot trees and hurl vehicles hundreds of yards. They can also drive straw into trees. Damage paths can be in excess of one mile wide to 50 miles long. In an average year, 1000 tornadoes are reported nationwide.

How do tornadoes form? 

Most tornadoes form from thunderstorms. You need warm, moist air from the Gulf of Mexico and cool, dry air from Canada. When these two air masses meet, they create instability in the atmosphere. A change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

What are some other factors for tornadoes to form?

Several conditions are required for the development of tornadoes and the thunderstorm clouds with which most tornadoes are associated. Abundant low level moisture is necessary to contribute to the development of a thunderstorm, and a "trigger" (perhaps a cold front or other low level zone of converging winds) is needed to lift the moist air aloft. Once the air begins to rise and becomes saturated, it will continue rising to great heights to produce a thunderstorm cloud, if the atmosphere is unstable. An unstable atmosphere is one where the temperature decreases rapidly with height. Atmospheric instability can also occur when dry air overlays moist air near the earth's surface. Finally, tornadoes usually form in areas where winds at all levels of the atmosphere are not only strong, but also turn with height in a clockwise or veering direction.

Cloud Types

Cloud Types common cloud classifications

Clouds are classified into a system that uses Latin words to describe the appearance of clouds as seen by an observer on the ground. The table below summarizes the four principal components of this classification system.

Latin Root		Translation		Example
cumulus stratus cirrus nimbus		heap layer curl of hair rain		fair weather cumulus alto stratus cirrus cumulonimbus

Further classification identifies clouds by height of cloud base. For example, cloud names containing the prefix "cirr-", as in cirrus clouds, are located at high levels while cloud names with the prefix "alto-", as in altostratus, are found at middle levels. This module introduces several cloud groups. The first three groups are identified based upon their height above the ground. The fourth group consists of vertically developed clouds, while the final group consists of a collection of miscellaneous cloud types.

Classifications

High-Level Clouds Cloud types include: cirrus and cirrostratus. Mid-Level Clouds Cloud types include: alto cumulus, alto stratus. Low-Level Clouds Cloud types include: nimbostratus and stratocumulus. Clouds with Vertical Development Cloud types include: fair weather cumulus and cumulonimbus. Other Cloud Types Cloud types include: contrails, billow clouds, mammatus, orographic and pileus clouds.