When was mt ruapehu formed

Mt Ruapehu is the largest active volcano in New Zealand and is located at the southern end of the Taupo Volcanic Zone. Three summit craters have been volcanically active in the last 10, years. The active vent is now beneath the crater lake of South Crater.

The crater lake contains warm, acidic water that is fed by snow melt. Ruapehu is a stratovolcano composite cone volcano made of successive layers of andesite lava and ash deposits. The mountain is surrounded by a ring plain of volcanic material from lahars, landslides and ash falls. Tephra ranging in size from dust ash fall to bombs and blocks are produced in every eruption.

Usually the crater lake causes magma to cool and fragment explode quickly and violently leading to fine ash eruptions. There are frequent lahars during eruptions or later due to collapse of the crater lake wall. As lahars descend valleys, sufficient momentum may be attained for a flow to climb up the river banks at bends in valleys and even flow up and over topographic barriers located directly in their path.

Figure 7: 25 September lahar near flow peak 9. From measurements afterwards, the upper lahar level was 4. C Barrett. Lahars are created by a variety of mechanisms. Water is essential to lahar formation. Large volumes of water are often stored in crater lakes e.

Crater Lake, Ruapehu and when the rim of a crater lake collapses or when eruptions occur through a lake, large volumes of water are released. If the crater lake is sited high on a volcano or at the summit, a fast moving lahar may be generated due to the fall in height. Pyroclastic flows have generated lahars as they mix with river or lake waters. Heavy rains on the flanks of a volcano may saturate loose materials which become unstable, fail and then flow as a lahar.

These may be particularly common for months to years after large eruptions when a thick blanket of ash coupled with vegetation destruction may lead to widespread failure of the saturated products.

Melting of snow and ice by a variety of processes including high heat flow from the ground or lava flows may create large volumes of water which may be temporarily stored in depressions or directly create lahars. Steam explosions have also triggered collapses of sectors of volcanoes that have generated lahars. The hazards from lahars are due principally to their unusual mobility. By tending to be channelled along lower ground, lahars are of greatest hazard in valleys or in depressions.

If sufficiently large, lahars may overtop river banks and spread outwards onto the surrounding landscape. Lahars are dense and fast which enables them to carry objects of tremendous size and weight. Buildings and vehicles may be demolished, buried or carried along with the flow. People caught by lahars are unlikely to survive as they become sucked into the flow and drown.

Some lateral erosion may occur leading to removal of embankments and channel side collapse. Although lahars do not generally travel as fast as pyroclastic flows they are often more fluid and may travel enormous distances, many times farther than the outer limits of pyroclastic flow distribution around Ruapehu.

Lahars may be initiated in minutes giving little warning of their impending arrival. Deposition of volcanic sediment form lahars in river channels leads to a reduced channel capacity and in consequence a greater likelihood of more flooding.

On the lower flanks of a volcano like Ruapehu it is also possible for lahars and floods to overflow into adjacent catchments and thus change from an expected flow path.

Lahars are not easily controlled or channelled, although many engineering schemes have attempted, with partial success, to reduce their destructive power. The distribution of volcanic debris avalanches, lahars and associated floods at Ruapehu in historical times, and over the last 10, years and 20, years is shown in Fig.

Figure 8: Areas inundated by lahars or volcanic debris avalanches and associated floods from Ruapehu. Tephra is a term that encompasses all the products of a volcanic eruption that are aerially ejected from a vent.

Tephra is subdivided into three dominant particle sizes, ash less than 2mm diameter , lapilli mm diameter and blocks or bombs greater than 64mm in diameter. Unlike the other forms of volcanic processes that travel close to the ground surface, tephra can be dispersed widely through the atmosphere. Tephra dispersal is principally governed by the height of an eruption column which may be up to 40 km high and the predominant wind directions and wind velocities.

The finest fraction, ash, is widely distributed for up to hundreds of kilometres and at high altitudes from the volcano. In contrast blocks and bombs are usually found within a few kilometres from source. Lapilli fall from eruption columns up to tens of kilometres from the volcano. The hazards presented by tephra may be considered as 1 the problem created by the physical presence of tephra and 2 the presence of potentially harmful substances adhering to tephra particles that create a poison or pollutant to water supplies and animal foodstuffs.

The effects are very much dependent on particle size, tephra thickness and distribution. Near to the vent "ballistic" projectiles may be metre-sized and may travel at great velocity causing injury to persons and property by direct impact or burial.

Asphyxiation may also result in areas of high ash deposition which may not be restricted close to the source. However, by far the greatest problem is ash in the home, at work, on highways, in water supplies, in the air, and where it mantles the ground from grazing pastures to airport runways that creates a major nuisance effect.

Downwind from source, tephra particles become finer and, as they fall and become redistributed by the wind, are able to penetrate cracks and crevices. Of immediate concern in a tephra eruption is the danger to public health and safety. Although inhalation of ash particles on infrequent occasions may be more of a discomfort than a health hazard, ash concentrations in the atmosphere exceeding a total suspended particle TSP concentration of 0.

This can lead to breathing problems despite the natural filtering mechanisms operating in the nasal passages, because particles finer than 0. People involved in clearing the ash and scientists investigating the eruptions may be exposed to high dosage rates. If free silica particles are abundant in the ash, the danger of silicosis is also increased in those exposed to high TSP concentrations. Incidence of diseases such as "industrial" bronchitis, acute and chronic obstructive pulmonary disease COPD or emphysema and asthma are likely to increase in areas where more than 10mm of ash falls, and more especially when greater than 50mm of ash deposition is experienced.

Susceptibility to these diseases depends on the condition of people being exposed to the ash, but clearly is greatest for heavy smokers and those with pre-existing respiratory diseases. The use of facemasks is the most effective way to reduce inhalation of particles less than 0. If protection devices are not available, dampened handkerchiefs are probably the next best screening material.

In areas of thick ash fall similar hazards will be experienced by domestic animals and agricultural livestock. Besides the direct effects of ash inhalation, there is also the secondary problem of ash covering vegetation and affecting the palatability of feed or even burying it completely.

Thus livestock on farmland and natural fauna would face impairment of bodily functions and could experience respiratory diseases, grinding down of teeth and starvation. In the eruptions of some fluorine toxicity was also experienced with pregnant sheep grazing ash-coated pastures.

The consequences of ash deposition on a variety of high value horticultural crops is very much dependent on the susceptibility of the plant. Larger leafed plants such as potatoes, tomatoes, lettuce and cauliflowers are likely to be most sensitive. Ash may accumulate on the soil surface and compact to form a water resistant crust that inhibits soil water infiltration and increases surface runoff with possible resultant erosion.

Remobilised tephra may lead to river aggradation and blockage of water intakes for both domestic consumption and hydroelectricity generation. Ash penetration of farm machinery can be a major problem. On farms with dairy shed equipment, a problem in any future eruption would be preventing ash particles entering milking equipment and clogging mechanical parts. Farm pumps would experience rapid wear on seals and bearings.

The use of settling basins to reduce grit flowing through pumps would alleviate this problem. Covering valuable machinery is another alternative. Heavy ash fall disrupts transport services and communications. Impaired visibility for drivers of motor vehicles can be a danger during eruptions. Volcanic ash is opaque in nature so visibility may be reduced to zero even with car headlights on.

In addition to the attrition effects on aircraft, particularly aeroengines, decreased visibility in the atmosphere and traction difficulties may prohibit aircraft from landing on or taking off from runways.

Ash deposition may interrupt telephone communications, and disrupt radio and electrical services as ash particles penetrate contact breakers and induce short circuiting. Intense electrical activity in and near the ash cloud may produce frequent lightning strikes on buildings and equipment. The sheer weight of thick tephra deposits on house roofs can lead to collapse if the tephra is not removed. The danger of roof collapse is related to the angle of pitch of a roof, with flat-roofed houses being at greatest risk.

As soon as dry tephra has been brushed or hosed from problem areas it immediately creates a secondary disposal problem around the building perimeter. If the tephra becomes wet it may form a slippery slurry and on redrying may harden like cement.

This may lead to blockage of storm water systems. Ultimately the tephra will enter waterways. Increased sediment loadings will affect town water supplies downstream and by sheer volume block water intakes, reduce the storage volume of channels and increase the likelihood of flooding. Contamination of water supplies can take a number of forms resulting from physical and chemical changes in water quality. The most common contamination problem results from the suspension of ash in water turbidity.

The influence volcanic ash has on water quality is highly variable. Water-soluble materials clinging to glassy and crystalline ash particles may be potentially harmful for drinking purposes, if in sufficient concentration.

These solutes may be strongly acid or alkaline. Under natural conditions these concentrations will quickly become diluted downstream. Based on the previous eruptive history of Ruapehu, a tephra hazard-zonation map has bee compiled with expected tephra thicknesses for 1 a small magnitude eruption e. Volcanic gases consist predominantly of steam H2O , followed in abundance by carbon dioxide CO2 and compounds of chlorine and sulphur. Minor amounts of carbon monoxide, fluorine and other compounds are also released.

Concentrations of gases will dilute rapidly away from a volcano and pose little threat to people more than a few kilometres from the active vent. Eruptions at Ruapehu volcano are accompanied by very high fluxes of acidic gas especially sulphur dioxide SO2.

This is because large quantities of these gases are extracted in Crater Lake from gas vents and fumaroles during non-eruption times and "stored" in the lake water until an eruption occurs. Other significant gases emitted by the volcano include carbon dioxide, hydrogen chloride and hydrogen fluoride.

The impacts of these gases on human health in distant communities are poorly studied. In contrast there is a clear problem on the volcano during eruptions and scientists working on Ruapehu during recent eruptions encountered dangerous concentrations of SO2 in A significant gas hazard is present in Crater Lake basin at most times.

During an eruption a portion of the ejected SO2 and hydrogen chloride and hydrogen fluoride dissolves in water droplets in the eruption plume to form aerosols droplets and tiny particles which rain out over the landscape with the ash.

This mixture often creates acid rain and an atmosphere haze known as "VOG" volcanic smog. Explosive eruptions at Ruapehu include a range of hazards that define an approximately circular zone of extreme risk to facilities and human life that extends about 2km from the centre of Crater Lake. The last major eruption was in after having shown signs of increased activity. The thick ash cloud was reportedly seen right across the North Island and, as it fell, blanketed the ground in a sand-like substance.

Since then, Mount Ruapehu has had a series of smaller, sporadic eruptions as well as plenty of warnings of heightened activity. Mount Ruapehu has two commercial ski fields, Whakapapa and Turoa which are the largest in New Zealand. To the east is Tukino ski field, a club-operated section of the mountain that is open for public use.

With the ski season approaching, Mount Ruapehu will come to life with the bustle of snow-seekers looking for a great day on the slopes. As the weather starts to cool down, the snowy white peaks will soon appear along the Tongariro volcanic zone. Tongariro National Park is so rich in history, culture and geology and this is the reason many visit the area.

A trip to the Tongariro region is full of excitement and outdoor adventure thanks to our resident volcanoes. As this is one of our busiest seasons, book with us in advance to secure comfortable, quality accommodation with easy access to and from each of the ski fields. Best of all, you can experience the Tongariro volcanic zone for yourself.

Call us today. Book Now! The history and geology of the Tongariro volcanic zone.