Q: Has the eruption at White Island caused an eruption at Tongariro (or vice versa)?
A: No, the magma systems of these two volcanoes are completely separate. The magma for each volcano is stored only a few kilometres below them, whereas the two volcanoes are about 220 km apart.

See also these useful FAQ responses from US Geological Survey on the topic:

Q: Is there an increased chance of Taupo Volcano erupting at the moment because of the eruptions at White Island and Tongariro?
A: GeoNet monitoring of Taupo Volcano shows that it is quiet, with no signs of unrest. The magma system at Taupo volcano is thought to lie between 5 and 20 kilometres below the ground, and is not linked to the magma systems of the currently active volcanoes. This means activity at White Island or Tongariro doesn’t cause activity at Taupo Volcano.

Q: What do the volcanoes of Taupo Volcanic Zone have in common?
A: The Taupo Volcanic Zone (TVZ), which includes the volcanoes from Mt Ruapehu to White Island, is part of a line of volcanoes stretching to Tonga. The TVZ is associated with the boundary between the Pacific and Australian Tectonic Plates. Plate boundaries stretch all the way around the Pacific, forming the Pacific Ring of Fire, home to many volcanoes. The Taupo Volcanic Zone includes the currently active Tongariro and White Island volcanoes, which are both driven by the same kind of plate tectonic process.

Q: Could we get a super-volcano eruption at Tongariro or White Island?
A: Super-volcano eruptions are generated by caldera volcanoes like Taupo, Okataina and Rotorua , whereas Ruapehu, Ngauruhoe/Tongariro and White Island are cone volcanoes that typically produce ash clouds (e.g. Ruapehu 1995/96) and sometimes lava flows. The volume of magma erupted during an eruptive episode at a cone volcano is typically less than 1% of that erupted in a super-eruption from a caldera volcano.

Q: Can the recent eruption at Tongariro lead to further eruptions at Tongariro?
A: There are 3 potential scenarios that the scientific community are assessing for future activity at Mount Tongariro. The scenarios are:

(1) The eruption was a one off eruption and the volcano will go back to sleep,
(2) The eruption was the initial eruption in a series of small eruptions, or
(3) The eruption was the precursor to larger, magmatic eruptions.

The first scenario is considered most likely at present (as of August 14th 2012). The volcano is being monitored for further signs of unrest by looking at visual observations, seismic activity, ground deformation, and chemical analysis of steam and gas output. Since the initial eruption, the output from the eruptive vents has been mostly sulphur-rich volcanic gas and steam, indicating that there is likely to be some magma involved in the system. Up-to-date information from monitoring by GeoNet can be found here.

Q: What is the difference between an ash and gas/steam plume?
A: When an explosive eruption occurs, rock fragments are torn from the walls of the vent and crater, and if there is magma involved, this is also fragmented into tiny pieces. This ash is propelled upwards by the heat and energy coming from the volcano in an eruption plume. This plume is carried downwind as the ash falls down to the ground, sometimes for hundreds of kilometres away from the volcano, and will appear as a dark grey colour.

A steam and gas plume will generally appear white in colour, but can sometimes have a yellow or blue tinge or be clear. These plumes are carrying volcanic gas, which may include hydrogen sulphide (causing a rotten egg smell), and steam. If the gas and steam plume mixes with rain it can form a weak version of acid rain.

Q: How is ashfall forecasted?
A: The ashfall forecast maps given in Volcanic Alert Bulletins (GeoNet) show the areas likely to experience ash falling on the ground if an eruption were to occur within six hours of the stated time period. The forecasts are based on the likely volume of volcanic output, and the forecasted direction of the wind. The wind vectors are obtained from MetService for the vertical profile directly above the volcano at a given time (usually 0600 and 1800 NZST).

Ashfall forecast maps are different to maps forecasting ash for airlines. The GeoNet ashfall forecast maps indicate where ash is likely to land on the ground, whereas the aviation maps (usually titled ‘Volcanic Ash Advisory’ from the Volcanic Ash Advisory Centre in Wellington) forecast ash plume locations in the atmosphere at elevations that aircraft are likely to be flying.

 The two maps can look different because of differences in low and high elevation wind directions. It is very important to make sure you know which of these two maps you are looking at before you take action in preparation for ash fall. The correct map for ashfall comes from GeoNet and is titled ‘Predicted Ashfall Area’.

The box on the side of the predicted ashfall area map is a graphic showing wind data. The numbers relate to the elevation above sea level in kilometres. The length of the arrow’s tail relates to the velocity of the wind, and the arrow head shows the direction it is going. In this example, the label “25 m/s” is a scale; if the wind vector line is as long as the arrow next to “25 m/s”, the wind speed is 25 m/s; if it is twice as long then the wind speed is 50 m/s.

Q: In case of future eruptions, what is the best source for emergency response information?
A: Local Civil Defence and local law enforcement are the primary source for information in the case of an emergency.

There are also two web pages that have been set up to guide communities that may be impacted by volcanic ash. They are produced in collaboration with the New Zealand ashfall impacts research scientists.

The first web page covers information including answers to questions such as: what is volcanic ash? Guidance for dealing with volcanic ash for homes, business and communities is also provided. There is also detailed information on impacts for agriculture, buildings, communications, power supply, transportation water supply etc. The web site is found here:http://volcanoes.usgs.gov/ash/

The second information source is for health issues related to volcanic ash:http://www.ivhhn.org/index.php?option=com_content&view=article&id=55&Itemid=61/

Q: What are the findings from the testing of volcanic ash samples collected from Tongariro?
A: Various aspects of the ash testing was done by labs at Massey, Victoria, and Otago universities and at GNS Science. It involved microscopic and chemical analysis. It showed there was very little 'new magma' in the ejecta, which suggests that the eruption was mostly gas-driven. This coincides with other observations that the event was largely a degassing episode. However, scientists say that the involvement of magma in the future cannot be ruled out.