Te ahi tipua me te wai puia Volcanic and hydrothermal activity

Volcanic and hydrothermal activity are natural geological processes driven by heat and pressure. Volcanic activity involves the movement of molten material (magma) to the earth’s surface. Hydrothermal activity occurs when water underground is heated by magma or hot rock.

Volcanoes and hydrothermal systems produce a range of hazards and have different levels of unrest and eruptive activity.

Volcanic unrest is increased activity at a volcano, that may lead to a volcanic eruption. Volcanic unrest can produce hazards on or near a volcano, such as volcanic earthquakes, land deformation, landslides, hydrothermal activity, and gas emissions. Some volcanic unrest can only be detected by monitoring equipment.

Most volcanic eruptions follow unrest, but not all unrest episodes lead to volcanic eruptions.

Volcanic eruptions are caused by magma (molten rock) moving beneath the surface of the Earth. Hydrothermal activity occurs when groundwater is heated by hot rock or magma.

Volcanic Explosivity Index (VEI) is often used to describe the size of a volcanic eruption. An eruption will be given a VEI score from 0-8, with 8 representing a very large eruption. The score is based on the amount of material ejected from a volcano during an eruption.

Hydrothermal activity is the release of water, energy, gas or other material at the surface. Hydrothermal systems are driven by magmatic processes related to volcanic activity or tectonic activity related to earthquake faults. Hazards from hydrothermal activity include hydrothermal eruptions and ground subsidence. 

New Zealand straddles the Australian and Pacific Plates on the “Ring of Fire” around the Pacific Ocean. The Ring of Fire contains most of Earth’s active volcanoes.

New Zealand has 11 active volcanic areas (above water). Eight are in Te Ika-a-Māui the North Island:

• Auckland Volcanic Field
• Northland (Bay of Islands and Whangarei Volcanic Fields)
• Ōkataina Volcanic Centre (including Tarawera)
• Rotorua Volcanic Centre
• Ruapehu
• Taranaki Maunga
• Taupō Volcanic Centre
• Tongariro Volcanic Centre (including Ngauruhoe, Te Maari and Red Crater)

Three are offshore (north of Te Ika-a-Māui the North Island):

• Kermadec Islands (Raoul and Macauley Islands)
• Tuhua/Mayor Island
• Whakaari/White Island

There are also many more underwater volcanoes in the Kermadec Volcanic Arc which is located between the North Island and Tonga.

Most of New Zealand's hazardous hydrothermal activity occurs in the Taupō Volcanic Zone, from Whakaari/White Island to Ruapehu. Some homes in these locations may be at greater risk from hydrothermal eruptions, ground subsidence and gas emissions.

In 2016, a spontaneous hydrothermal event in Ohinemutu, Bay of Plenty, generated steam eruptions and geysers. Hydrothermal eruptions happen reasonably regularly in Ohinemutu at the lake edge. Usually this occurs as bubbling up of water and mud from the lake bottom, rather than creating geysers.

Volcanic eruptions can produce a range of hazards, some close to the volcano and others that can affect areas hundreds of kilometres away.

Near-volcano hazards:

• pyroclastic flow: extremely fast-flowing mixtures of hot gases and volcanic rock that form when eruption columns or lava domes collapse. They flow down, and sometimes beyond, the slopes of the volcano, and are highly destructive.
• ballistics: pieces of lava and rock that range from centimetres to tens of metres in diameter.
• land deformation: movement of the ground surface, such as swelling, sinking, or cracking.
• landslides (debris avalanches): caused by the collapse of unstable rock, mud, sand, and soil, from the side of a volcano. At the largest scale, collapses of whole volcano sections can occur, which has happened at Taranaki many times in the past.
• lava flows: streams of molten rock that pour from an eruption site and flow down valleys or across land.
• wildfires: can be ignited by volcanic eruptions (especially lava flows) and can set fire to buildings, infrastructure, and vegetation. They can spread quickly, particularly in dry conditions and in urban areas.

Far-reaching volcano hazards:

• ash fall: small (less than 2mm) fragments of rock and glass produced by explosive eruptions transported downwind. Ash can be blown hundreds of kilometres, but the layer will be thinner further away from the volcano. Breathing airborne volcanic ash can cause short-term symptoms such as a cough and sore throat and may have more serious health effects for some people and animals.
• gases and aerosols: plumes of volcanic gases such as carbon dioxide (CO2), hydrogen chloride (HCl), and sulphur gases (H2S and SO2) blown downwind. Gases and aerosols can be harmful to health, irritate eyes, skin, and affect breathing.
• lahars (volcanic mudflows): hot or cold, dense mixtures of water, rock, mud, sand, and soil, that travel rapidly downstream.

Hydrothermal areas have hot, pressurised water and gases near the earths surface. They can be unpredictable and dangerous.

• hydrothermal eruptions: sudden, explosive bursts of steam, water, mud, and rock
• fumaroles: holes which emit superheated gas and steam under pressure
• boiling mud pools: pools of hot acidic mud that can cause severe burns
• hot pools: naturally heated water that can reach scalding temperatures, sometimes with toxic gases
• geysers: hot springs with intermittent water eruptions, accompanied by steam

Near-volcanic activity hazards can be dangerous and very destructive to property, impacting 3–5km from the vent, and extending up to 10–20km away from the eruption site.

• Lava and pyroclastic flows can damage or destroy property, and can set fire to buildings, infrastructure, and vegetation.
• Ballistics can be ejected from the volcano’s vents along fast, cannonball-like trajectories and can be highly damaging to buildings.
• Land deformation can directly damage homes, cause landslides, and increase the risk of flooding as the ground moves.

Far-reaching eruption hazards, extending beyond 10-20km from the eruption site, are most commonly disruptive rather than destructive.

• Ash fall can be thick enough to collapse roofs and cause structural damage to buildings, especially if the ash becomes wet and heavy.
• Lahars, rapidly moving dense mixtures of water, rock, mud, sand, and soil, can extend tens of kilometres from a volcano and cause damage to buildings and other structures including infrastructure.
• Volcanic gases can cause health issues, and when combined with rainfall, cause acid rain that can accelerate the rusting of metal surfaces, including those on property, and contaminate drinking water.

The most common parts of your home that can be damaged include:

• roof, gutters, and rainwater tanks
• electrical equipment
• sewerage pipes
• foundations, from tremors or hydrothermal activity

• Learn how to make your home saferopen_in_new
• Search your address in the Natural Hazards Portal to find out which hazards may affect your property.
• Read more about volcanic hazardsopen_in_new and how they can affect people and places.
• Check that you have the right insurance in placeopen_in_new, including home insurance that may qualify you for natural hazards cover.
• Check your local council website for information about local hazards and emergency planning in your area.