7 August 2012
Tongariro eruption and advice
The eruption of Mt Tongariro seems to have had minimal impact on farm pasture and stock drinking water. GNS’ predicted
ashfall map, issued before Civil Defence cancelled the Tongariro Volcano National Advisory this afternoon, indicated ash
fell largely on National Park or forested areas. This map is available from GNS, meanwhile, Radio NZ reported some places inland from Napier, had ‘about 1 mm of ash’ by mid-morning.
Volcanic events are unpredictable so famers should review preparedness:
The Ministry for Primary Industries has a good preparedness note downloadable by clicking here (we have summarised some points below). Meanwhile, the United States Geological Survey (USGS) has an excellent paper on how to rehabilitate farms affected by ash; ‘about 1 mm’ means the impact of ash on farms is negligible according to
the USGS.
We do not yet know if the eruption of 6 August 2012 is a one-off event or the beginning of a more active cycle. This is
a timely reminder to review farm preparedness if you farm within the Waikato, Bay of Plenty (due to White Island),
Rotorua-Taupo, Taranaki, Ruapehu, Wanganui, Tararua, Gisborne-Wairoa, Manawatu-Rangitikei, Hawke’s Bay and the
Wairarapa.
Short-term weather forecast:
The MetService is predicting rain and showers for the central and lower North Island over the next few days. This will help to
dissipate ash from last night’s eruption.
Planning ahead:
§ Check your supplies of general emergency supplies including reserves of water, food, batteries, candles, and gas/fuel
for at least three days. Ensure you have ample supplies of suitable facemasks/respirators (and spare canisters), gloves
and goggles for your family and employees
§ Ensure farm insurance cover is adequate and covers crop, livestock and/or pasture insurance for volcanic impacts
§ Maintain a resilient power supply by checking power lines and poles are in good working order and free from
overhanging branches
§ Purchase generator(s) or ensure you can access generators. As mobile phone sites have limited battery capacities,
check if the sites near your farm have points for the connection of generators
§ Ensure the key equipment you may need can be run off PTO’s (tractor power take-offs)
§ Make certain you have a non-electrical air compressor in good working order; these are highly useful for cleaning ash
from machinery and equipment
§ Keep water distribution systems well-maintained; connect distribution systems with separate sources into a single
network and have maximum storage in covered water supplies where possible. Ensure sumps, drainpipes and drain grills are
kept clear
§ Ensure you have adequate stock water storage in tanks that can be distributed without electrical pumps, for example,
by locating tanks so that water can be gravity-fed
§ Take steps to protect the farm’s household water supply by installing a disconnect valve on roof-fed rainwater tanks
and stockpiling bottled water
§ Have access to a 4WD vehicle to ensure mobility
§ Have ample stocks of fuel along with engine and milking machine filters, lubricating oil, brake and hydraulic fluids
and seals. As ash is fine and highly abrasive, maintenance schedules may well be measured in hours
§ Locate ash dump sites away from critical farm areas and consider what can be used to cap the ash deposits, e.g soil
may prevent ash being remobilised by wind or water erosion.
Post-eruption:
§ Prioritise farm activities by developing a list of facilities that must be kept operative
§ The physical effects of ash on stock usually predominate over chemical impacts. However, toxic effects due to the
presence of fluoride, selenium and sulphur can also be a problem with fluoride toxicity being the most common. The
Ministry for Primary Industries has a good preparedness note, including details on Flurorsis, available by clicking here. Fluoride in ash becomes soluble with rain, which is forecast for the next few days
§ The cleaning of roofs, roads, tracks and paved surfaces should be a priority to prevent roofs collapsing, to stop the
movement of ash and for simple access
§ Dampen down fine ash with a small amount of water and sweep with a broom. Too much water will result in glue-like slurry that may set hard, block drains and
make removal more difficult
§ Be careful to conserve water supplies.
§ Regularly check pumps, filters and water intake structures for blockages and signs of damage
§ Accelerate the changing of filters, seals and fluids to prevent damage to equipment from fine abrasive ash
§ Check the resilience of key utilities and reconstruct if necessary
§ An up-to-date analysis of soil fertility indicators can help inform the best management approach for soil
rehabilitation.
Ash effects and rehabilitation strategies:
These are based on observations from Mount St. Helens (1980), Ruapehu (1995-6) and other eruptions (source: USGS).
Please remember this paper was originally written for an American audience but provides useful guidance.
Thin burial (< 5 mm ash)
§ Impacts of ash negligible
§ Rehabilitation of the land not necessary
§ In the short-term, ash is washed and consolidates to 1-2 mm
§ Increased supplementary feed may be required if stock are off their feed.
Moderate burial (25 - 30 mm ash)
§ Pastures destroyed from ash burning so rehabilitation will be similar to that after a severe dry period
§ Pastures can be re-established either through conventional cultivation or undersowing
§ Where ash is up to 25 mm deep, incorporation of the ash through ploughing is the most suitable method
§ Hill country rehabilitation will be slower, as material cannot be incorporated into the soil profile
§ Rainfall will improve the rate of recovery as the ash is eroded
§ Oversowing with fertiliser will be necessary, due to the inherent lower fertility of the soils and also where pastures
are weakened/destroyed by the ash
§ Extra supplements are required to maintain stock numbers until pastures recover
§ Greenfeed crops and high producing annual ryegrasses could be established if an eruption occurred late summer. This
would provide increased feed in the winter until permanent pastures could be established
§ It is important to maintain farm operations, especially in terms of providing good quality water and maintaining farm
machinery
§ The costs of re-establishing pastures after an eruption with moderate burial will be similar to a severe drought.
Moderate burial (25 - 30 mm ash)
Rehabilitation will be greatly influenced by the time of year of the ashfall and the nature of the ash
Late winter/early spring in temperate climates:
§ The most critical period for dairy, sheep, and beef; pasture covers are low and supplementary feed has largely been
used (there is also calving and lambing)
§ Management options will be to mob stock, move them through longer pasture areas of the farm to shake/remove ash off
the plants. These areas can then be grazed with some supplementary feed
§ It will be difficult to procure sufficient grazing to de-stock affected farms at this time of the year. However, some
de-stocking of the farm may be possible by sending stock to the works or for grazing in other parts of the country
§ Paddocks that had been intended for cropping or pasture renewal could be cultivated and sown in fast growing annual
crops, including annual ryegrasses, and feed grain
§ Soil fertility is likely to decrease in the short term, requiring higher fertiliser inputs but not necessarily for all
elements.
Summer/autumn in temperate climates
§ Management options are eased by the ability to de-stock lambs, prime cattle and cull dairy cows to the works. Reserves
of hay or silage are at the greatest and greenfeed crops such as maize, choumollier or swedes will be of sufficient
maturity to supply a substantial amount of feed
§ Good quality water is essential, increased water pump maintenance and cleaning of troughs will be required for farms
on deep well bores and reticulated systems
§ Farms taking supplies from streams or dams, provision of good quality water for both human and stock consumption will
be more difficult. Outside assistance may be required in the short-term (until streams clear and dam water can be tested
clear of toxic chemicals)
§ Rehabilitation of any farm will be dependent on the financial resources of the farmer and the robustness of the farm
business.
Thick burial (50-100 mm ash)
§ Rehabilitation will be influenced by the farm contour, availability of suitable machinery, finance and human resources
§ Ash does not dissolve or percolate into the soil profile, therefore tillage with high inputs of fertiliser is required
(providing a medium for establishing ryegrass/white clover pastures)
§ Ash falls of 50 mm will have serious financial implications in the year of the ashfall and also the following season.
Land able to be cultivated
§ Ploughing as deep as 20 cm gives best results, as the ash layer is mixed with underlying soil. Incorporation of ash
will still result in changes to the soil characteristics, such as greater soil moisture, lower fertility and
permeability. Large scale cultivation will be expensive
§ Costs include re-grassing, fertiliser and high machinery maintenance costs due to the abrasive nature of the ash
increasing wear and tear
§ Rehabilitation of land affected by ash is similar to development of sand country where the initial requirement is
establishment of any species tolerant of the conditions to stabilise the ash and build up fertility
§ Re-establishment of pastoral species is dependent on the nature of the ash. With very acidic ash, liming could be
required, along with high fertiliser inputs to create a soil medium, conducive to pastoral growth
§ Initially, acid tolerant species may need to be planted and species more tolerant of severe conditions
§ These species tend to be lower yielding than the existing ryegrass and clover pastures. Once soil fertility and
organic matter levels increase, more productive species may be established.
Land not able to be cultivated
§ Rehabilitation will be a slow and costly process
§ Oversowing of low fertility species with fertiliser inputs may be required.
§ It may be un-economic for land to resume pastoral use; other land use may be appropriate
§ Rehabilitation will be dependent on the financial resources of the farmer, which may be extremely limited after the
financial toll of the eruption.
Stock
§ May require de-stocking of the land for at least six months
§ Rehabilitation will require re-stocking, but may not be physically possible where the eruption devastates a large area
§ Culling of stock may be the only option, which will result in a loss of valuable stock of high genetic merit
§ Until the ash consolidates, quality water for stock will be scarce
§ Extra expense will be incurred in maintaining water pumps (affected by the abrasive nature of the ash)
§ The physical removal of the ash from buildings, yards, tracks will be required.
Very thick burial (100 - 300 mm ash)
§ Rehabilitation extremely difficult and likely to take generations.
§ Soil sterilised below ash
§ Ash too deep to be incorporated using conventional cultivation techniques, including ploughing, discing or rotatilling
§ Restoration dependent on removal of the ash layer or a much longer time frame of re-colonisation of the ash layer
§ Re-colonising agents need to be adapted to harsh environments and will vary with climate
§ Initially, restoring basic facilities such as roads, water supply, power, and effluent systems are required before
restoration can occur
§ Immediate requirement is relocation of affected residents and provision of adjustment programs.
Extremely thick burial (> 300 mm ash)
§ Land un-farmable for many generations
§ Rehabilitation at an extreme cost
§ Medium-term (20 to 40 years), rehabilitation unlikely to be economic
§ Long-term, alternative land uses need to be explored (i.e. forestry)
§ Immediate requirement, relocation of the affected residents and provision of adjustment programs.
For more information
ends