Explaining emergency eventsTe whakamārama ohotata

Explaining earthquakes

The Science of Earthquakes

Our Earth is not a solid rock but is made up of a series of different layers. These are the crust, the mantle, the inner core and the outer core. The crust is the outside layer that we live on and is a series of solid plates that float on the liquid mantle below.

The plates are constantly moving due to convection currents occurring in the mantle layer. This layer is liquid magma and heats up and cools down resulting in convection currents.

Some of these plates move apart. Such as the plates running down the middle of the Atlantic Ocean.

Some plates move directly into each other. Such as the collision of the Australian Plate with the Pacific Plate forming the Southern Alps in the South Island.

Others form subduction zones, where one plate moves under the other. This occurs in New Zealand in the North Island, causing a line of volcanoes and geothermal areas. 

When plates move we get small cracks called fault lines. As fault lines move there can be either a gradual release of energy or a sudden release of energy resulting in earthquakes.

The Richter Scale measures the size of an earthquake. It is a measure of the energy released. When earthquakes are deep in the Earth their energy is the same. But the shaking does not feel as strong as shallow earthquakes.

The amount of shaking you feel is another way to describe earthquakes. We call this the intensity. The intensity is stronger when you are close to the earthquake source and when the earthquake is shallow. It decreases the further away you are. We describe earthquakes by the energy released, which is their magnitude. We also describe them by how strong the shaking feels, which is their intensity.

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Explaining floods

There are many parts of Aotearoa that a flood could affect. In fact, floods are the most common emergency event around the country.

The science of floods

The water cycle is when water circulates from clouds to the soil to streams to rivers to the oceans and then returns to the clouds.

When a lot of rain falls, it can be too much for the soil to soak up and streams can fill up. When streams and rivers fill up faster than they can flow out to sea, the water runs onto land and causes a flood. Urban flooding can also happen when there is too much water for the storm water drains to clear. 

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Explaining storms

The Science of Thunderstorms

Above the crust is a layer of air that is essential to all living things, called the atmosphere. Our atmosphere divides into different layers. Closest to the ground is the troposphere, which is about 8–15 kilometres thick. This is the layer where most of our weather occurs as it is the most dense.

The air in the atmosphere is always moving as it heats up and cools down. This causes convection currents that we experience as wind. Clouds are also a visible sign of these convection currents. This means that the air becomes unstable. When unstable air meets lots of moisture, there is the potential for thunderstorms.

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Explaining volcanoes

The Science of Volcanoes

Volcanoes are mostly found along the borders between plates in the Earth’s crust. The Earth’s plates move around because they are floating on top of a layer of liquid rock called magma. Magma forms the layer we call the mantle.

This layer is under a lot of pressure. If there is a gap in the plates, the liquid rock can be forced out. Just like when you shake a bottle of fizzy drink and then open it.

When the magma is forced out above ground, it cools to form solid rock. This is lava. Lava can flow in sheets to form layers of new rock, but it can also build up hills and mountains, which we call volcanoes.

New Zealand’s active volcanoes are on the North Island or in the sea near the North Island. Volcanoes can produce lava as well as ash, lahar and a range of different gases. Some of these extremely poisonous.

The shape and size of a volcano depends on the materials in the magma, the force of the explosions and its age. Volcanoes can be extinct, dormant or active.

The most common volcanic hazard is ash. It is very scratchy because volcanic ash is tiny pieces of sharp rock. When an eruption happens, the wind can carry ash hundreds of kilometres. During the volcanic eruption of Mt Ruapehu in 1996, a thin layer of ash covered farms, cars and buildings.

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