EGF 2013
European Grassland Federation
Akureyri, June 23-26 2013
Volcanic impacts on grasslands – a review
Olafur Arnalds
Agricultural University of
Iceland
Based on a review in
Advances in Agronomy
121: 331-380
Mount St. Helens (1980; USA) is
the best studied volcanic impact.
However many other notable
examples of research.
Volcanic imacts very common in
Iceland
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)
Mostly associated with plate boundaries
Also stationary „hot spots“ where magma
rises from the mantle (mantle plumes)
The hot spot
(circle, assumed center)
Tephra - ash
Tepra is the correct term for all airborne volcanic
deposits.
Volcanic ash is fine tephra (< 2mm)
Impact type
Ground disturbance
Aftermath, common year ranges
Examples
Hawaii; Mt Etna; Laki,
Iceland; Paricutin 1943-1990
(Mexico)
A
Lava flow
Destruction – new surface.
New soil development, climate
dependent, 100 ‘s – > 1000 yrs
B
Pyroclastic flow; lahar;
jökulhlaup
Total destruction – new surface
New soil development, climate
dependent, 100’s – > 1000 yrs
Mt. St. Helens Pinatubo,
Philippines
Excessively thick
tephra >70 (100) cm
Very thick tephra
Near total destruction – new
surface; massive erosion
New soil development, climate dependent
, 100’s – >1000 yrs
Krakatau 1883
Kamchatka
Agriculture and rangeland
destruction; massive erosion
20- >100 yrs for recovery, shorter for
forests
Katmai 1912, Alaska
Temporary disturbance; erosion
and dust emission
Recovery 30-150 yrs on rangelands,
shorter in forest, “permanent” in Arctic
and desert areas, temporary disruption of
cultivation (1-10 yrs)
Mt.St. Helens 1980, Hudson
1991,Chile Paricutin 19431990 (Mexico)
Moderately thick
tephra; 1 – 10 cm
Little and temporary disturbance,
some erosion and dust emission
Temporary impact, species changes, 1050 yrs for recovery of natural systems,
positive nutrient responses$
Mt. St. Helens 1980.
Common in Iceland
Thin tephra;
Little and temporary disturbance,
erosion and dust
Sometimes positive nutrient responses,
negative impact on crusts
Common in Iceland, Mts.
Hekla and Katla
Traces (< 1 mm)
Negligible ground disturbance
Positive nutrient responses Temporary
fluoride hazards
Widespread in volcanic areas
Gas / ash into tropo- and
stratosphere
Secondary impacts
Aeolian redistribution
Dust production
Regional – global cooling;
eruption size dependent
Cool periods, crop failures, yrs
Laki, Iceland; Pinatubo,
Philippines;
Abrasion and burial of plants,
dust pollution
Continuous wind erosion dependent on
thickness, 1–20 yrs
Eyjafjallajökull; Iceland in
general
K
Fluvial redistribution#
Plugs up river channels, new
areas for aeolian processes
Flooding, dust production, 1–10 yrs
Eyjafjallajökull, Pinotubo,
Mt.St.Helens
L
Landslides#
Dangerous in urban areas
Temporary disruption of natural systems,
1-20 yrs
Vesuvius
C
D
20 – 70 (100) cm
Thick tephra
E
F
G
H
I
J
10 – 20 cm
0.1 – 1 cm
Ksudach,
Distribution of the “H3” Mt. Hekla eruption
(2800 BP), deposition thicknesses in cm. Total
tephra: 11-12 km3 (Larsen & Thorarinsson,
1977).
Adapted from
Einarsson, 1991 and
Thorarinsson, 1961.
Isopach im cm.
Wilson et al. 2011. Bulletin of Volcanology 73.
Hudson (Chile) 1991 Eruption
Volcano
Eyjafjallajökull
(Iceland)
Ruapehu (New
Zealand)
Pinatubo
(Philippines)
Hudson (Chile)
Year
VEI Total Examples of impacts
km3
2010
0.2
Temporary air traffic shut down, vegetation burial, dust
problems > 2 yrs.
1995-96
3
<01
Severe fluoride toxicity problems, livestock killed.
1991
6
4-5
Temporary cooling, water erosion and lahars.
1991
5
4.3
Wide range of impacts on agriculture, dust problems.
Mount St. Helens
(USA)
Hekla (Iceland)
Krakatau (Indonesia)
Tambora (Indonesia)
1980
5
1.5
Pyroclastic flows, debris avalanches, lahars and tephra.
1947
1883
1815
4
6
7
1
10
100
Tephra damage on rangelands, fluoride problems.
Tsunami, tephra burial, human casualties.
Catastrophic near volcano, > 100 000 human casualties,
global cooling with snow in England in June.
Laki (Iceland)
1783
6
1610BC
7
73 k
8
Santorini (Greece)
Toba (Indonesia)
15-19 570 km2 lava buries farmland, gas releases cause
toxicity and cooling resulting in famine in Iceland and
Europe.
60
Destruction of Minoan culture, global draught and
(125) famine.
2700 ‘Volcanic winter’ on Earth. Human genetic bottleneck?
Factors affecting impact and ecosystem recovery
after tephra deposition.
Volcanic
Thickness of
tephra
Biotic
Ecosystem
Climatic and Seasonal
Rainfall (amount and
Pasture/ rangeland, intensity), wind speeds
forest, Arctic, alpine, (intensity of dry storms)
desert, wetlands
Nature of deposits Local vegetation
Temperature annual,
growing season etc.
Chemistry, texture, Height and
Includes also
composition,
hardness,
temperature gradients
compaction, toxicity Biological legacy
with height
Adaption to burial Time of year with
Distance from
volcano
largest impacts at the
I.e. some plants
Influencing grain
beginning of growing
adapted to burial,
size and thickness
season, least in the fall
some vulnerable
and on snow
Animals carrying
Snow cover and
seeds
intensity of snow melt
events
Landcape/Surface
Landscape
characteristics and
mosaic, seed sources
etc
Surface steepness,
surface roughness,
surviving vegetation
etc.
Isolation distance
from propagule
sources
Volcanic deposits : Andosols
- fertile soils of volcanic regions
Type of soils
dependent on
climate, chemistry,
time etc.
Santorini
France
Iceland
Azores
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
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 1998. Canadian Journal of Botany 76.
Responses of cold/Arctic systems to burial
in Iceland (controlled experiments)
Mólendi Hálslón
Heath
625 m
elevation
A.
Moss 425 m
elevation
Mosaþemba Blöndulón
100
100
100
80
80
80
60
60
60
40
40
40
20
20
20
0
0
0
100
100
30
Heildarþekja %
Total cover %
Heath 425 m
elevation
Mólendi Blöndulón
Þykkt áfoks:
0
1
2
4
8
Vascular plants %
% þekja háplanta
B.
80
80
60
60
40
40
20
20
0
0
0
40
40
100
30
30
20
20
20
10
Mosses %
% þekja mosa
C.
80
60
40
10
10
0
0
0
6
25
5
20
4
15
3
10
2
5
1
20
Lichens %
% þekja fléttna
D.
4
2
0
0
0
2
4
6
0
0
2
4
Ár frá upphafi tilrauna
6
0
2
4
6
YRS
cm
cm
cm
cm
cm
Biological Soil Crusts are
a major component of
many rangelands / grazing
lands
Extremely susceptible to
ash deposition
Photo: Ása L. Aradóttir
Jarðvegsfræði, ÓA
Thin tephra is leached into
the sward. Extreme danger
of F toxicity
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; 20-40 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.
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).
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):
>100 000 t /km2 >1.000.000 reported
Fluvial /aeolian deflation rates > 5 cm / yr
Aeolian flux rates >1000 kg/m
Eyjafjallajökull 2010
Example of vegetation
height
In the
beginning
Grass 14. maí 2010
Ph. Johann Torsson
Desert May 14 2010
Ph: Johann Thorsson
Skógaheiði
May 14
June 23
July 3
t/ha
Barren
442
130
0
Grass
589
529
559
In the fall
Eyjajallajökull – example of tephra on
low vegetation in a small eruption
Extreme storm episode
V
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
45
15.5
21.7
55,293
331
442
II
62
15.3
19.1
10,225
61
59
III
122
17.8
23.8
160,949
964
474
IV
148
14.4
21.5
19,023
114
46
V
397
22.5
38.7
1,589,559
9528
1440
VI
192
17.4
24.3
124,073
743
232
VII
405
14.1
20.1
9832
59
9
Over 10 tons transported over 1 m wide
line during one storm.
Dust storms after eruptions are
common.
The role of roughness
and vegetation cover
Grímsvötn 2011 ash covering rough lava
surface covered with moss.
May 2011.
August 2012. (Two summers later)
i) Rained into the moss
ii) Blown away as dust
iii) Redistributed into the
depressions (wind and water)
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.
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.
Type of Andosol dependent on chemistry of ash and climate
(and many other factors)
Increased pH
Increased weathering intensity
Allophanic
Intensly weathered
Moderate weathering
MHC
Andisols
Time
Vitric Andisols
Iceland
Entisols
Vitric - tehpra
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
Direction of ash
deposition form large
rhyolitic eruptions in
Mt Hekla during
Holocene
How large are eruptions?
The VEI scale (but km3 often most informative)
VEI km3
Examples
Icelandic examples
Hekla 1947, Eyjafjallajökull
2010
Hekla 1104, Surtsey 1963-1966
4
>0.1
5
>1
Mt St Helens 1980
6
>10
Krakatau 1883, Mt Pinatubo 1991
7
>100
Tambora 1815; Santorini (1620 BC)
8
>1000 Yellowstone 640k yr, Toba 74 k yr
Hekla 2800BC, Laki 1783,
Eldgjá 834,
A range of impacts
Lava flows
Lahars, pyroclastic flows,
jökulhlaups
Tephra (ash) deposition
Fluoride toxicity
Atmospheric influences
Secondary impacts (erosion, dust,
landslides)
Grasslands – Rangelands – Volcanic ash
A range of conditions/potential; affecting survival and recovery
Stable grassland
Arid regions
Rangeland in Iceland
Grassland?
S Arizona
Collapsed grassland
Arid regions
S New Mexico
E Iceland
Destroyed systems in
Iceland (volcanism and
grazing)
S-C Iceland
Model for perennial
grasses.
Sand burial
Maun, 1998. Canadian Journal of Botany 76.
Recovery
I
II
III
IV
Favorable
conditions
1
Unfavorable
conditions
10
100
1000 yrs
May 2011
August 2012