What are Geohazards

The word geohazard comes from two words:

1. Geo – from the word ‘geological’ meaning from the earth
2. Hazard – something that poses a risk to property, place or life

So ‘geohazards’ means the risk of damage from a geological process.

Sometimes hazards are not easy to see. For example, we wash our hands to avoid germs (biohazards) even though they are too small to see. We are told that some foods are poisonous (a biohazard) so we don’t eat them.

All geological hazards (geohazards) could be called dormant until they are triggered.

When the hazard occurs it may then be called an event, accident, emergency, incident, or disaster. The study and monitoring of geohazards helps us to better prepare ourselves and helps us respond to these geological events when they do occur.

Geohazards can be small features that have an impact only on their local area such as a small landslide that partially blocks a road or track, through to large earthquakes that affect whole cities. They can also be very large events that have a widespread impact such as large tsunami.

Types of geohazard

Geohazards include:

• landslides
• earthquakes
• tsunamis
• volcanoes
• lahars
• hydrothermal eruptions

Common geohazards in New Zealand

New Zealand is geologically active. This is because it sits across the boundary between two tectonic plates. These moving plates create huge forces that have shaped our amazing landscape; pushing up mountains, carving out lakes and rivers and creating our rugged coastline. These forces are still shaping the land today and can also cause frequent earthquakes, landslides, volcanic eruptions, hydrothermal activity and even tsunami.

Earthquakes

Earthquakes are caused when rocks break due to the stress of the moving tectonic plates. Large earthquakes near towns or cities can cause great damage and sometimes loss of life. For this reason it is important for New Zealanders to know how to prepare for earthquakes.

Tsunami

A tsunami is a series of powerful ocean surges caused by movement of part of the sea floor – often by an undersea earthquake or landslide. Most tsunamis are similar to very strong, fast tides, rather than waves. The larger ones can travel a long way inland. Much of the damage from tsunamis is caused by the debris carried in the water.

Volcanoes

When magma reaches the earth’s surface a volcano is formed. A volcano will erupt pieces of rock and magma (ash) and release steam and gases. New Zealand’s volcanoes are often active and are always monitored, for example Ruapehu, Tongariro and White Island. Ash from eruptions can spread over large distances so can affect people living a long way from the eruption. Hazards can also happen close to active vents.

Lahars

A lahar is a volcanic mudflow. When moving, a lahar looks like a mass of wet concrete carrying pieces of rock. Lahars can be different sizes and move at different speeds. Lahars can cause widespread damage.

Eruptions may start lahars by quickly melting snow and ice on a volcano or moving water from a crater lake. Lahars can also be formed by heavy rainfall during or after an eruption, when volcanic ash is washed off the volcano. Some of the largest lahars begin as landslides.

Hydrothermal activity

Hydrothermal systems are found where there is volcanic activity. The heat from the volcanic activity heats the local ground water to create the geothermal activity. Most of New Zealand’s hydrothermal activity occurs in the Taupō Volcanic Zone.

Hydrothermal activity includes hot springs, geysers and warm ground. If these become unstable eruptions can occur. Ground can become unstable and dangerous gases can form.

Landslides

A landslide is a movement of soil and rock down a slope. Landslides often happen because of earthquakes, volcanic eruptions and floods (rainfall).

Landslides are common in New Zealand. Large landslides in towns and cities can cause thousands of dollars in damage and threaten lives.