Hurricanes form over warm ocean waters. Sometimes they strike land. When a hurricane reaches land, it pushes a wall of ocean water ashore. This wall of water is called a storm surge. Heavy rain and storm surge from a hurricane can cause flooding.

Once a hurricane forms, weather forecasters predict its path. They also predict how strong it will get. This information helps people get ready for the storm.

There are five types, or categories, of hurricanes. The scale of categories is called the Saffir-Simpson Hurricane Scale. The categories are based on wind speed.

The National Hurricane Center on Thursday issued a hurricanewatch for the southernmost part of Florida, the first such alert Irma has prompted in the continental United States. A storm surge watch, which warned of potentially life-threatening levels of water, was also issued for the southern part of the state, an area that includes the Florida Keys, which a day earlier had begun evacuations.

Irma’s Category 5 force pinwheeled through the Caribbean, leaving a wake of leveled neighborhoods, ravaged seafronts and at least 10 dead, according to government officials and news reports. The storm is grinding onward toward the Bahamas with winds hitting 180 mph and higher gusts registered, according to the hurricane center, which warned of storm surges capable of swallowing huge sections of the coast.

After the Bahamas, Irma’s expected path takes aim at Florida, including the ribbon of cities, dense suburbs and swampland that are home to more than 6 million people from Palm Beach to Miami-Dade counties.

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.

Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock!

What causes earthquakes and where do they happen?

The earth has four major layers: the inner core, outer core, mantle and crust. (figure 2) The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth. (figure 3) Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.
%

When floods happen in an area that people live, the water carries along objects like houses, bridges, cars, furniture and even people. It can wipe away farms, trees and many more heavy items.

Floods occur at irregular intervals and vary in size, duration and the affected area.

It is important to note that water naturally flows from high areas to low lying areas. This means low-lying areas may flood quickly before it begins to get to higher ground. 

In this lesson, we shall see more about what causes flooding, the types of flooding, some effects of floods and what we can do before, during and after floods occur.

When osmosis happens, water moves from the side of the membrane with a lower amount of osmotic pressure to the side of the membrane with the higher amount. An important example of osmosis is the movement of liquid (solvent) molecules across a cell membrane into a cell with a higher solute concentration. Osmosis is a fundamental part of cell biochemistry, but also has mechanical applications and usages.

Hypotonic describes the less concentrated solution. An isotonic solution is when the concentration is equal on both sides of the membrane. Hypertonic describes the more concentrated solution. When there is a hypotonic solution outside the cell, and hypertonic solution inside, the cell gets swollen and distorted.

The plasma membrane of a cell is semi-permeable, which means it lets small molecules pass through, but blocks larger molecules. The membrane also has ports or gateways which get certain macromolecules through. This is active transport, which uses energy and is selective.