Volcanic impacts on grasslands a review

Transcription

1 EGF 2013 European Grassland Federation Akureyri, June Volcanic impacts on grasslands a review Olafur Arnalds Agricultural University of Iceland

2 Based on a review in Advances in Agronomy 121: Mount St. Helens (1980; USA) is the best studied volcanic impact. However many other notable examples of research. Volcanic imacts very common in Iceland

3 Volcanic activity is extremely common! About 1545 active volcanoes on Earth 9000 eruptions have been catalogued 70 volcanoes are active each year Mt Redoubt, Alaska (1990), (USGS- Wikipedia)

4 Mostly associated with plate boundaries Also stationary hot spots where magma rises from the mantle (mantle plumes)

5 The hot spot (circle, assumed center)

6 Tephra - ash Tepra is the correct term for all airborne volcanic deposits. Volcanic ash is fine tephra (< 2mm)

7 Impact type Ground disturbance Aftermath, common year ranges Examples A Lava flow Destruction new surface. B C D E F G Pyroclastic flow; lahar; jökulhlaup Excessively thick tephra >70 (100) cm Very thick tephra (100) cm Thick tephra cm Moderately thick tephra; 1 10 cm Thin tephra; cm Total destruction new surface Near total destruction new surface; massive erosion Agriculture and rangeland destruction; massive erosion Temporary disturbance; erosion and dust emission Little and temporary disturbance, some erosion and dust emission Little and temporary disturbance, erosion and dust H Traces (< 1 mm) Negligible ground disturbance I J Gas / ash into tropo- and stratosphere Secondary impacts Aeolian redistribution Dust production K Fluvial redistribution # Regional global cooling; eruption size dependent Abrasion and burial of plants, dust pollution Plugs up river channels, new areas for aeolian processes L Landslides # Dangerous in urban areas New soil development, climate dependent, 100 s > 1000 yrs New soil development, climate dependent, 100 s > 1000 yrs New soil development, climate dependent, 100 s >1000 yrs 20- >100 yrs for recovery, shorter for forests Recovery yrs on rangelands, shorter in forest, permanent in Arctic and desert areas, temporary disruption of cultivation (1-10 yrs) Temporary impact, species changes, yrs for recovery of natural systems, positive nutrient responses $ Sometimes positive nutrient responses, negative impact on crusts Positive nutrient responses Temporary fluoride hazards Cool periods, crop failures, yrs Continuous wind erosion dependent on thickness, 1 20 yrs Flooding, dust production, 1 10 yrs Temporary disruption of natural systems, 1-20 yrs Hawaii; Mt Etna; Laki, Iceland; Paricutin (Mexico) Mt. St. Helens Pinatubo, Philippines Krakatau 1883 Kamchatka Katmai 1912, Alaska Ksudach, Mt.St. Helens 1980, Hudson 1991,Chile Paricutin (Mexico) Mt. St. Helens Common in Iceland Common in Iceland, Mts. Hekla and Katla Widespread in volcanic areas Laki, Iceland; Pinatubo, Philippines; Eyjafjallajökull; Iceland in general Eyjafjallajökull, Pinotubo, Mt.St.Helens Vesuvius

8 Distribution of the H3 Mt. Hekla eruption (2800 BP), deposition thicknesses in cm. Total tephra: km 3 (Larsen & Thorarinsson, 1977). Adapted from Einarsson, 1991 and Thorarinsson, 1961.

9 Isopach im cm. Wilson et al Bulletin of Volcanology 73. Hudson (Chile) 1991 Eruption

10 Volcano Year VEI Total Examples of impacts km 3 Eyjafjallajökull (Iceland) Ruapehu (New <01 Severe fluoride toxicity problems, livestock killed. Zealand) Pinatubo Temporary cooling, water erosion and lahars. (Philippines) Hudson (Chile) Wide range of impacts on agriculture, dust problems Temporary air traffic shut down, vegetation burial, dust problems > 2 yrs. Mount St. Helens Pyroclastic flows, debris avalanches, lahars and tephra. (USA) Hekla (Iceland) Tephra damage on rangelands, fluoride problems. Krakatau (Indonesia) Tsunami, tephra burial, human casualties. Tambora (Indonesia) Catastrophic near volcano, > human casualties, global cooling with snow in England in June. Laki (Iceland) km 2 lava buries farmland, gas releases cause toxicity and cooling resulting in famine in Iceland and Europe. Santorini (Greece) 1610BC 7 60 Destruction of Minoan culture, global draught and (125) famine. Toba (Indonesia) 73 k Volcanic winter on Earth. Human genetic bottleneck?

11 Factors affecting impact and ecosystem recovery after tephra deposition. Volcanic Biotic Climatic and Seasonal Landcape/Surface Thickness of Ecosystem tephra Nature of deposits Chemistry, texture, hardness, compaction, toxicity Distance from volcano Influencing grain size and thickness Pasture/ rangeland, forest, Arctic, alpine, desert, wetlands Local vegetation Height and composition, Biological legacy Adaption to burial I.e. some plants adapted to burial, some vulnerable Animals carrying seeds Rainfall (amount and intensity), wind speeds (intensity of dry storms) Temperature annual, growing season etc. Includes also temperature gradients with height Time of year with largest impacts at the beginning of growing season, least in the fall and on snow Snow cover and intensity of snow melt events Landscape characteristics and mosaic, seed sources etc Surface steepness, surface roughness, surviving vegetation etc. Isolation distance from propagule sources

12 Volcanic deposits : Andosols - fertile soils of volcanic regions Type of soils dependent on climate, chemistry, time etc. Santorini France Azores Iceland

13 Forest grassland understory Humid/temperate grassland Arid grassland Cold/Arctic grassland Biotic Ecosystem Pasture/ rangeland, forest, Arctic, alpine, desert, wetlands Local vegetation Height and composition, Biological legacy Adaption to burial I.e. some plants adapted to burial, some vulnerable Animals carrying seeds

14

15 Plants respond to burial in different ways (model for sand) III. Stimulation of growth, sand species. Plants show positive responses to burial up to a critial limit. II. Zero response, up to a critical limit I. Species not adapted to burial show immediate negative response Maun Canadian Journal of Botany 76.

16 Responses of cold/arctic systems to burial in Iceland (controlled experiments)

17 Total cover % A. Heildarþekja % Heath Mólendi Hálslón 625 m elevation Heath 425 m elevation Mólendi Blöndulón Moss 425 m elevation Mosaþemba Blöndulón Þykkt áfoks: 0 cm 1 cm 2 cm 4 cm 8 cm B Vascular plants % % þekja háplanta C Mosses % % þekja mosa D Lichens % % þekja fléttna Ár frá upphafi tilrauna YRS

18 Biological Soil Crusts are a major component of many rangelands / grazing lands Extremely susceptible to ash deposition Jarðvegsfræði, ÓA Photo: Ása L. Aradóttir

19 Thin tephra is leached into the sward. Extreme danger of F toxicity

20 Grassland response (reasonable grass sward) (generalizations) Extreme deposits (>30 cm): system destroyed, fate depends on redistribution. Usually coarse tephra. Thick deposits (10-30 cm): Temporary; yrs to get 80% back. Redistribution important. Medium deposits (2-5 cm): Recovers within 10 yrs. Some redistribution. Thin deposits (0.5-2 cm). Recovers within years, often positive overall. Little redistribution. Traces: Nutrient input, depends on chemistry. No redistribution.

21 Positive effects of traces Basaltic ash: provides cations to soils and maintains ph. Recharges nutrient depleted systems. Rhyolitic ash: less nutrients. Productivity of Icelandic ecosystems closely related to rate of deposition of volcanic materials (more fertile, higher ph closer to the volcanic rift-zones).

22 REDISTRIBUTION by EROSION Wind erosion, Water erosion, Landslides Some of the highest erosion rates measured on Earth Fluvial sediment yield > (Mt Pinatubo, Mt St Helens 1980): > t /km 2 > reported Fluvial /aeolian deflation rates > 5 cm / yr Aeolian flux rates >1000 kg/m

23 Eyjafjallajökull 2010 Example of vegetation height

24 In the beginning Grass 14. maí 2010 Ph. Johann Torsson

25 Desert May Ph: Johann Thorsson

26 Skógaheiði In the fall May 14 June 23 July 3 t/ha Barren Grass

27 Eyjajallajökull example of tephra on low vegetation in a small eruption

28 V Extreme storm episode

29 Episode Length Wind speed m s -1 No of Calculated transport saltation min Average $ Max $ kg m -1 kg m -1 hr -1 pulses I , II , III , IV , V ,589, VI , VII Over 10 tons transported over 1 m wide line during one storm.

30 Dust storms after eruptions are common.

31 The role of roughness and vegetation cover Grímsvötn 2011 ash covering rough lava surface covered with moss. May 2011.

32 August (Two summers later) i) Rained into the moss ii) Blown away as dust iii) Redistributed into the depressions (wind and water)

33 Alien species Interaction between tephra disturbance and the presence of alien species: Can cause dramatically altered pathways of recovery with dominance of alien species. The literature most often consider the effects to be overall (very) negative.

34 Conclusions The frequency of volcanic impacts is high! The influences are important, both on ecosystems and culture. The nature of the impact is very dependent on the ecosystem potential to recover which is heavily influenced by land use. Redistribution of volcanic ash is a major factor in determining the effects of volcanic eruptions Impacts can be positive with moderate ash inputs (nutrients) and by the formation of fertile Andosols.

35 Type of Andosol dependent on chemistry of ash and climate (and many other factors) Allophanic Increased ph Moderate weathering Increased weathering intensity Intensly weathered MHC Andisols Time Vitric Andisols Iceland Entisols Vitric - tehpra

36 Grasslands / Rangelands Grasslands: dominated by grasses (wikipedia). Rangelands: Primarily native vegetation, rather than plants established by humans. Often grass dominated. Both grazed and non- grazed. Dominated by relatively low growing vegetation, especially heavily grazed arid and Arctic/cold systems

37

38

39 Direction of ash deposition form large rhyolitic eruptions in Mt Hekla during Holocene

40 How large are eruptions? The VEI scale (but km 3 often most informative) VEI km 3 Examples Icelandic examples 4 >0.1 Hekla 1947, Eyjafjallajökull >1 Mt St Helens 1980 Hekla 1104, Surtsey >10 Krakatau 1883, Mt Pinatubo 1991 Hekla 2800BC, Laki 1783, Eldgjá 834, 7 >100 Tambora 1815; Santorini (1620 BC) 8 >1000 Yellowstone 640k yr, Toba 74 k yr

41 A range of impacts Lava flows Lahars, pyroclastic flows, jökulhlaups Tephra (ash) deposition Fluoride toxicity Atmospheric influences Secondary impacts (erosion, dust, landslides)

42 S New Mexico S-C Iceland Grasslands Rangelands Volcanic ash A range of conditions/potential; affecting survival and recovery Stable grassland Arid regions Rangeland in Iceland Grassland? S Arizona E Iceland Collapsed grassland Arid regions Destroyed systems in Iceland (volcanism and grazing)

43 Model for perennial grasses. Sand burial Maun, Canadian Journal of Botany 76.

44 Recovery I II III IV Favorable conditions Unfavorable conditions yrs

45 August 2012 May 2011