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Introduction |
Ash fall can adversely affect crops and livestock in a variety of ways, but it is very difficult to predict exact consequences and associated costs of potential ash damage or mitigation measures. This is especially true for large explosive eruptions that result in ash fall over large areas and for a series of small eruptions that occur repeatedly over months to years. The information in this section identifies a range of known effects of ash fall on acricultural crops and livestock that can serve as a rough guideline for what can be expected . The information below is incomplete, however, and is not applicable to all situations because of the wide range of ash thickness and type and status of crops that can exist in different parts of the world at the time of an explosive eruption. Furthermore, there is a lack of detailed accounts of the effects of ash fall on individual farms in different regions, including the ways that farmers and governments have attempted to reduce the damaging consequences to their crops and livestock.
| Additional information and case studies are needed to improve the usefulness of this section. If you have information and knowledge of case studies that can help the Ash Web Team prepare new material on the effects of ash on agriculture and livestock, please contact the Ash Web Team. Through your support and contributions, this Web site can be significantly improved to help farmers and others deal with future volcanic ash falls. |
Survival of livestock exposed to ash falls || feed availability || water quality || seasonal influences || ash toxicity || other factors || evacuation || |
 Pasture land for sheep near Mount Ruapehu, New Zealand;
photo courtesy of GNS, New Zealand.
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When ash falls destroy pastures, livestock need to be supplied with all of their feed in order to survive in the short-term. The supply of dry feed must be maintained until the livestock are either evacuated or slaughtered, or pasture is re-established. Even with very light ash falls that do not destroy existing pastures, animals may need to be provided with uncontaminated feed. For example, if the ash contains a high level of fluorine adsorbed onto the tiny particles and livestock consume both ash and fluorine, there is a risk of fluorosis. Livestock near Ruapehu volcano (photograph) were affected by fluorosis when grazing grass contaminated by ash from the 1995-1996 eruptions—more than two thousand lambs and ewes died after eating ash-contaminated pasture. The first sheep deaths began nine days after 1-3 mmof ash fall, and continued for 7-10 more days. |
Where there is a significant ash fall, clean water will likely be in short supply. Natural water sources and man-made ponds may be temporarily contaminated by ash, and water-pumping equipment can be damaged by the abrasive rock particles (covering with tarps may provide protection). Restoring quality water supplies for livestock is typically a high priority if livestock are to remain on land affected by ash fall.
The 1995-1996 eruption of Mt. Ruapehu in New Zealand (temperate region, 39o S latitude) clearly showed that a thin ash fall in early spring can have a significant impact on sheep, beef, and dairy farms. On dairy farms, milk yields were severely depressed in early lactation (yields were actually depressed during the entire lactation). On sheep and beef farms, lamb and calf survival and thrift were poor as ewes and beef cows reduced or stopped lactating. Wool quality is likely to be severely affected where sheep are close to shearing; the entire wool clip could be rejected.
Ash falls may be poisonous to livestock and result in clinical diseases, including hypocalcaemia, fluorosis, forestomach and intestinal damage, and secondary metabolic disorders.
Fluorine aerosols in the eruption column and cloud that become attached to fine ash particles pose a potentially significant threat to livestock. As smaller ash particles have large surface areas relative to their mass, the fine particles can transport significant amounts of soluble fluorine onto pastures far downwind from an erupting volcano. The smallest ash particles travel the greatest distance from a volcano; thus a thin layer of fine ash only 1 mm thick can contain potentially toxic amounts of fluorine. Livestock ingest fluorine directly as ash is consumed along with pasture feed and soil.
Fluorine poisoning has occurred in several Icelandic eruptions, and was recently responsible for the deaths of over 2,000 grazing animals following the 11 October 1995 eruption of Ruapehu, New Zealand (Cronin and others, 2003). An immediate toxic dietary intake of Fluorine is >100 μg g -1 for grazing animals, but a lower concentration may cause sickness. Cattle can tolerate around 40 μg F g -1, and sheep up to 60 μg F g -1. Under normal winter conditions in New Zealand sheep ingest 260-275 g of soil per day, and sheep foraging for feed covered with ash are likely to take in even more (Cronin and others, 2003).
Chronic fluorosis causes death. Before death, however, the poisoning causes lesions in the nose and mouth, and hair to fall out around the mouth. Other symptoms include nutritional and stress related diseases, convulsive seizures, pulmonary odema, and kidney and liver changes. A tooth condition known as “spiking” may also occur, causing outgrowths to develop on molars and making chewing difficult.
When toxic levels of fluorine on pastures are identified, it is recommended that livestock are removed from the affected areas until sufficient rainfall has leached the fluorine from the ash.
A high sulphur concentration adhered to the ash may induce copper and cobalt deficiencies in the long term.
When pastures are subjected to ash falls and remobilization of ash by wind, evacuation of livestock to areas with good quality feed and water may be prudent. Even after evacuation, long-term inhalation of ash and exposure to fluorine may result in reduced productivity. In some cases, stock may not recover in the long-term, with humane slaughtering being the best option.
Where ash falls affect a large area, evacuation of stock would be extremely difficult due to the logistics of moving large numbers of stock and sourcing feed in areas unaffected by the ash. This may result in large losses of livestock through dehydration and starvation.
Effects on Pasture || ash thickness || ash composition || secondary impacts || |
Ash falls greater than 10-15 cm (4-6 in) typically result in the complete burial of pastures and soil. Where soil burial is complete, the soil will become sterile because it is deprived of oxygen; existing pasture species and crops and most soil micro-organisms will die. Where ash is as thick as about 5 cm (2 in), plant survival and re-growth will be dependent on several factors, including the chemical nature of the ash, compaction of the ash after the eruption, degree of continuing disturbance, amount and reliability of rainfall, and length of plant stalks at the time of ash fall.
The impact of weather conditions on ash thickness
The survival of pastoral plants is influenced by the timing of rainfall after ash covers an area. Wet ash will consolidate to approximately one-third of the original thickness of dry ash. If it rains soon after an eruption (within 2-3 days) plant survival may be improved because of the compaction. On steep slopes, rain will wash ash into gullies and low-lying basins, leading to increased erosion and deposition in some areas (for example, deposition often occurs at the base of steep hillsides). Wind erosion may also pile ash into "ash dunes," if the ash is not already consolidated or incorporated into the soil profile.
Duration of ash burial
When ash falls lead to the complete burial of pastoral plants for 5-7 days, it is likely that all plants will die, as also occurs with heavy silting and flooding. Even if ash is removed within 5 days, plants may still die from burning if the ash is acidic.
Impacts on plants and soil from increasing ash thickness (based on limited historical observations or recent eruptions). The impact on some aspects, including soil composition in particular, will vary depending on ash composition.
Thin burial (< 5 mm ash)
- No plant burial or breakage.
- Ash is mechanically incorporated into the soil within one year.
- Vegetation canopies recover within weeks.
Moderate burial (5 - 25 mm ash)
- Buried microphytes may survive and recover.
- Larger grasses are damaged but not killed.
- Soil underneath remains viable and is not so deprived of oxygen or water that it ceases to act as a topsoil.
- Vegetation canopies recover within next growing season.
Thick burial (25 - 150 mm ash)
- Completely buries and eliminates the microphytes.
- Small mosses and annual plants will only be present again in the local ecosystem after re-colonization.
- Generalized breakage and burial of grasses and other non-woody plants;
some macrophytes of plant cover do not recover from trauma.- Large proportion of plant cover eliminated for more than one year.
- Plants may extend roots from the surface of the ash layer down to the buried soil, thereby helping to mix the ash and the buried A horizon. This is generally accomplished within 4-5 years.
- Vegetation canopy recovery takes several decades.
- Mixing of new ash into the old soil by people or animals greatly speeds recovery of plants.
Very thick burial (> 150 mm ash)
- All non-woody plants are buried.
- Burial will sterilize soil profile by isolation from oxygen.
- Soil burial is complete and there is no communication from the buried soil to the new ash surface.
- Soil formation must begin from this new "time zero."
- Several hundred (to a few thousand years) may pass before new equilibrium soil is established, but plants can grow within years to decades.
The acidity and nature of the ash (and leachates derived from the ash) varies between volcanoes and eruptions. Ash falls can lead to elevated soil sulphur levels and lowered soil pH. These changes in soil composition can reduce the availability of phosphate and other essential minerals and alter the soil's characteristics to such an extent that arable crops and pasture plants will not survive. Where there is acid rain following an eruption, pastures will be scorched and die.
Ash interaction with soil will have variable effects on pH, soil nutrients, capacity for cation exchange and micro-organism activity dependant upon the ash composition and leachate composition. To date little research has been published discussing these dynamics in detail.
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Pastural land in the Waikato Region, near the Taupo Volcanic Zone, New Zealand (Photo from GNS collection) |
Ash falls also affect insect populations, which are severely limited by ash falls greater than 2.5 cm (1 in). This may have a beneficial effect if pastoral and crop-pest populations are reduced due to the ash. Highly mobile insects, many of which have a dense covering of body hairs which can trap the tiny ash particles, such as honey and pollination bees, are more susceptible to ash than smooth-bodied insects such as beetles.
Fine ash can also serve as an effective mulch, improving water retention of soil.
Effects on forestry |
Young forests are most at risk from ash fall; stands of trees less than 2 years old are likely to be destroyed by ash deposits thicker than 100 mm (Neild and others, 1998). Ashfall alone is not likely to kill mature trees, but the accumulated weight of ash can break large branches in cases of heavy ashfall (>500mm). Defoliation of trees may also occur, especially if there is a coarse component of ash-sized particles or larger tephra and during heavy ash fall.
Impacts on forests are not expected to be significant until ashfall exceeds 100 mm. Branch damage may begin to occur in younger trees at around this level, with an increase in damage occurring as levels of ash increase. Access to forests will also be disrupted as roads may be blocked. Little long term damage is expected to ensue. Depths of around 500 mm of ash or more will cause major damage to forests. Extensive branch breakages will occur, and access to forests will be severely impeded. Access will not be possible at all for logging trucks. The area will be reusable, but the existing forest environment will be substantially altered, the burial of young trees a major part of this. Planting directly into basaltic ash is possible for many species, including Pinus Radiata. Planting directly into more silicic ash such as rhyolite is however more problematic, due to nutrient issues such as nitrogen and calcium deficiency (Neild and others, 1998).
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Plantation forestry on the slopes of Mt Etna during the 2002 eruption, unaffected by several millimetres of fallen ash; photo courtesy of S. Barnard. |
Effects on arable crops || plant development || weight of ash || Grain and cereal |
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Horticultural land in Hawkes Bay, New Zealand, downwind of the Taupo Volcanic Zone. (Image from GNS collection) |
Periods when crops are most at risk (from research in the temperate regions of New Zealand): (Neild and others, 1998)
Pea: from emergence until end of flowering.
Squash: during the initial stages of growth and flowering.
Tomatoes: during seed emergence and flowering stages.
Sweetcorn: during the early stages of growth.
Pipfruit has three danger periods:
Stonefruit is also susceptible at the same times as pipfruit, except that the early fruit development period is 4-6 weeks after blossoming, when sensitive fruit skins could be damaged, and show russet or deformation in severe cases.
- During blossom where severely acidic ash (pH less than 3) could burn plant tissue and result in poor pollination.
- 6 to 8 weeks after blossoming, when the skin of fruit is particularly sensitive.
- Later stages of development when fruit is prone to cosmetic blemishing.
Kiwifruit is also at risk at, and 6-8 weeks after, blossom. There would also be a problem at harvest time. As kiwi fruit cannot be washed prior to packing, the hairy nature of the fruit would make ash removal very difficult.
Grapes have three main periods when damage could occur:
- Flowering, when acidic ash could burn plant tissues, reduce pollination and reduce bunch fill.
- Fruit development, where ash deposits would block sunlight and reduce quality.
- Harvest, where ash deposits would be a contaminant with the extra acidity of the ash possibly having a significant impact on wine quality. Ash would have to be removed prior to harvesting by washing and allowing bunches to dry (not economically feasible in Etna case study).
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Mixed agricultural land including abundant vineyards in the Gisbourne region of New Zealand, downwind of the Taupo Volcanic Zone. (Image from GNS collection) |
Citrus fruit
The 2002 eruption of Mount Etna, Italy, resulted a light ash fall in Catania (3 mm). The light dusing of ash nevertheless adhered to the skin of citrus, which rendered fruit unfit for juice production because it was not economically feasible to separately clean each fruit before processing.
Ash from Etna volcano on the surface of citrus fruit made it uneconomical to produce juice because it was too expensive to clean the fruit (image courtesy of La Sicilia).
The weight of ash on leaves affects plant survival, increases harvesting costs, and reduces yield. Lucerne and pea crops, regardless of stage of growth, would either fail or have poor yields from ash falls of 10 mm (0.4 in) or greater. These plants have abundant delicate leaves and stems which are easily damaged by ash, which can reduce the rate of photosynthesis and make the crop susceptible to lodging.
Grain and cereal crops (especially corn)
The timing of the ash fall will affect the chances of survival of grain and cereal crops. For example, when corn is in a vegetative period during the first two months of growth, light ash falls are unlikely to affect the expected yield. Heavy ash falls, however, bury much of the plant and change the soil characteristics sufficiently to result in crop failure. The most critical period for corn yields is between three weeks before tasselling to two weeks after pollination. Even light ash falls during this period could result in barren stalks and crop failure. Damaged stalks are also more susceptible to disease, which may also reduce yields.
Corn requires many heat units for a crop to reach maturity. An eruption could delay crop maturity if sunshine hours were reduced during the eruptive period. ash fall near crop maturity will make harvesting difficult and reduce the quality of grain. Ash collected within and among the spikes will cause some contamination of the harvested grain. A high proportion of ash will be removed in the cleaning procedures already used in flour mills if ash falls are light.
Rainfall interacting with volcanic gas within the ash plume may produced acids which fall as acid rain. Continued degassing at the vent may lead to ongoing acid rain even after ash fall ceases.
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Acid rain damage to coffee plantation leaves 15 km downwind of Poàs volcano, Costa Rica. Frequent rainfall in the region mixes with volcanic gas to produce acid rain. (Peterson and Tilling, 2000) |
Case Studies || New Zealand || Italy || |
As a result of a less than 5 mm (0.2 in) ash fall on the Rangitaiki Plain (Taupo) during the 1995 Ruapehu eruption, approximately 2,000 ewes and lambs (2.5% of the area's sheep population) were killed by eating ash-affected pastures. Autopsies of the dead animals suggest fluorine poisoning or pregnancy toxaemia as the cause of death. Three Ayrshire dairy cows died at Atiamuri in June 1996. It was reported that they had stopped eating and showed signs of lethargy after swallowing quantities of ash; toxic levels of fluorine were found in the dead animals' blood. The Department of Conservation also reported the death of a number of wild deer in the Kaimanawa Ranges, located downwind from Ruapehu, following the two largest October 1995 eruptions (possibly up to 5% of the sika deer population). Livestock losses from the eruption of Ruapehu in 1995 were greatest in lactating ewes, grazing short pasture.
During the eruption, ash falls of 2 mm on pastoral land elevated soil sulphur levels and lowered soil pH by 0.2 - 0.3 units compared to pre-eruption values. One benefit was the reduction in sulphur requirement in annual fertilizer applications for many farms.
The crops grown in this area consist largely of citrus fruits, vegetables and grapes. All of these were ready to be harvested during the course of the 3 month eruption. Local produce was still sold in markets, but a covering of ash had to be washed off. This was not an easy task as the ash adhered to the fruit to such an extent that a simple rinse under a hose would not remove it.
Grapes needed to be washed individually before consumption to avoid ingesting fine ash. This effectively ruined the grape crop economically, even though the fruit itself was not damaged. This was the case for citrus fruit.
In some cases the skin of the fruit was reportedly pitted, however it was the adherence of the ash to the skins that again contributed much to the economic ruin of the fruit. Also, the usual mechanical processing of the fruit was stopped because the abrasive nature ash would have damaged machinery. Furthermore oranges destined for fruit juice production could not be used, as the inclusion of skin/peel in the manufacturing of juice was not possible with the coating of ash that was difficult to economically remove. Half of the orange crop in the province of Catania was destroyed by ashfall. Most of the orange crop received less than 3 mm of ash.
Italy’s federation of farmers also estimated about 80 percent loss of vegetables (unspecified sorts, but mostly leafy crops) over both the immediate area around Etna (the province of Catania) and in the neighbouring province of Siracusa. Seventy-five percent of agricultural jobs were also lost as produce could not be harvested. Total estimated cost to the region was 140 million euros.
Rehabilitation options for pasture and arable crops |
The ability to rehabilitate pastoral land and arable crops is mainly dependent on the thickness of the ash covering. The following table summarizes some of the options available at different thickness' of ash.
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Options depending on ash thickness and season
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| Thin burial (< 5 mm ash) |
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| Moderate burial (25 - 30 mm ash) |
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| Moderate burial (25 - 30 mm ash) |
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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
Summer/autumn in temperate climates
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| Thick burial (50-100 mm ash) |
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Land able to be cultivated
Land not able to be cultivated
Stock
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| Very thick burial (100 - 300 mm ash) |
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| Extremely thick burial (> 300 mm ash) |
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Cook, R.J., Barron, J.C., Papendick, R.I., and Williams, G.J., 1981, Impacts on agriculture of Mount St Helens eruption: Science, v. 211, p. 16-22.
Cronin, S.J., Hedley, M.J., Neall, V.E., and Smith, R.G., 1998, Agronomic impact of ash fallout from the 1995 and 1996 Ruapehu Volcano eruptions, New Zealand: Environmental Geology v. 34, p. 21-30.
Cronin, S. J., Neall, V. E., Lecointre, J. A., Hedley, M. J. and Loganathan, P. (2003) Environmental hazards of fluoride in volcanic ash: a case study from Ruapehu volcano, New Zealand Journal of Volcanology and Geothermal Research, vol.121, p.271-279
Folsom, M.M., 1986, Ash on range and forest lands of eastern Washington: Local erosion and re-deposition, in (eds needed) Mount St Helens: Five years later: Eastern Washington University Press, p. 116-119.
Gregory, N.G., and Neall, V.E., 1996, Volcanic hazards for livestock: Outlook on Agriculture, v. 25 (2), p. 123-129.
Thorarinsson, S., 1979, On the damage caused by Volcanic eruptions with special reference to ash and bases, in Sheets, P.D. and Grayson, D.K. (eds.), Volcanic activity and human ecology: Academic Press, New York, p. 125-159.
Neild, J., O'Flaherty, P., Hedley, P., Underwood, R., Johnston, D., Christenson, B., and Brown, P., 1998, Agriculture recovery from a volcanic eruption: MAF Technical paper 99/2. (Available online at http://www.maf.govt.nz/mafnet/rural-nz/emergency-management/volcanoes/volcano-erruption-impact/volimpact-18.htm).
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