The Iceland Volcano Thread

MJohnston wrote: »

Look on the brightside, at least the ash will make their land extremely fertile in the future

Options depending on ash thickness and season
Based on observations from Mount St. Helens (1980), Ruapehu (1995-6) and others. Possibly most applicable to temperate countries.

Thin burial (< 5 mm ash)
Impacts of ash negligible.
Rehabilitation of the land not necessary.
In short-term, ash is washed and consolidates to 1-2 mm.
Increased supplementary feed may be required if stock off their feed.

Moderate burial (25 - 30 mm ash)
Pastures destroyed from ash burning, rehabilitation is similar to the 25-50 mm scenarios; otherwise, 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 thick, 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 fertilizer 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 where the eruption occurred late summer, to 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 are similar to a severe drought.

Moderate burial (25 - 30 mm ash)
Rehabilitation will be greatly influenced by the time of year of the ash fall and the nature of the ash.

Late winter/early spring in temperate climates

Most critical period for dairy, sheep, and beef (pasture covers are low and supplementary feed has largely been used).
Management options will be to mob stock up, move them through longer pasture areas of the farm to shake/remove ash off the plants. These areas can then be grazed with some brought supplementary feed such as meal and hay if available.
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, feed oats and barley.
Soil fertility is likely to decrease in the short term, requiring higher fertilizer 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 corn, 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 fertilizer 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 ash fall and also the following season.

Land able to be cultivated

Ploughing as deep as 20 cm (8 in) 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, fertilizer 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 stabilize the ash and build up fertility.
Re-establishment of pastoral species, dependent on the nature of the ash. With very acidic ash, liming could be required, along with high fertilizer 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. For example, Marram grass, lupins, Yorkshire Fog and Lotus.
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 fertilizer 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 6 months.
Rehabilitation will require re-stocking, but may not be physically possible where the eruption devastates a large area.
Slaughtering 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, roadways will be required. See removal methods.

Very thick burial (100 - 300 mm ash)
Rehabilitation extremely difficult and likely to take generations.
Soil sterilized 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-colonization of the ash layer.
Re-colonizing agents need to be adapted to harsh environments and will vary with climate.
Possible re-colonizing agents are Lupins and Lotus species (that fix nitrogen) along with Marram grass.
Initially, restoring basic facilities such as roads, water supply, power, and effluent systems are required before restoration can occur.
Immediate requirement, relocation of the 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.