ISNS 4359
EARTHQUAKES AND VOLCANOES
Spring 2005
Steve Bergman, Instructor
Lecture 23. Volcanism, Global Climate Change, and Extinctions
Plutarch suggested the 44 BC Etna eruption dimmed the Sun; and caused the resulting cooling that caused crops to
shrivel, producing famine in Rome and Egypt. Ben Franklin suggested the 1783 Laki Iceland eruption produced
European dry fogs, and the cold winter of 1783-4. David Keys’ book Catastrophe (1999) suggested the6th century
Dark Ages were caused by global effects of an Indonesian eruption; Ken Wohletz (2000) suggested this was an
eruption of a 50 km diameter proto-Krakatau caldera.
Climate-average state of weather over months to years. Periodic changes in earth’s orbital characteristics (eccentricity
of orbit-100,000 yr cycle, tilt-41,000 yr cycle, and wobble of spin axis-20,000 yr cycle) have major effects on climate.
Large volcanic eruptions can also impact global climate.
Atmosphere Surface T averages ~15C (range –89 to 48C); ~33C warmer than a simple black body due to
greenhouse warming by H2O, N2O, CO2, CH4, O2, & O3.
Troposphere (T~ -65C, @ 10 km) balance of convective surface heating & radiative cooling;
Rate of temperature decline with elevation = Dry Lapse Rate –6.5C/km.
Stratosphere (T~ -5C @ 50 km) ozone (O3, 10-300 ppb) absorbs sun's UV & IR radiation.
Mesosphere (T~ -9010C @ 80 km) decreased O3 production & increased rate of cooling to space.
Thermosphere (T~70C @ ~120 km, 700 C @ ~250 km) heating by ionization and photolysis of N2 & O2.
Major volcanic eruptions inject dust and aerosols (microscopic liquid or solid particles as small as <10 -4 mm) to heights
of >20 km into the stratosphere for over a year. These particles reflect sunlight and result in a net Earth surface cooling.
Aerosol clouds from these eruptions circled globe in 2-3 weeks, eventually settle over 1-5 years.
Volcanic eruptions release gases such as H2O, CO2, SO2 into the atmosphere. SO2 - most important climatic cooling
effects; reacts with OH and H2O to form H2SO4, interacting the most with short and long wave solar radiation.
H2O, CH4, & CO2 are important greenhouse gases and contribute to global warming. Stratosphere warming due to
volcanic greenhouse gases is less important than Troposphere cooling due to overlying ash reflecting solar radiation.
Particles >2 microns (10-3 mm) fall at rates of >30 km/yr.
Volcanic HCl and SO2 also reduce stratospheric ozone, leading to increased UV radiation at surface (skin cancer-bad).
Stromboli (last 2 millennia) emits an average of 140 tonnes HCl & 600 tonnes of SO 2 per day [largest point source of
tropospheric air pollution in Europe]-source of dry fogs of Mediterranean documented between 1300-1900
Pinatubo (1991) 30 Mtons SO2 , ~5 km3 ash, solar radiation decreased ~30%, N Hemisphere cooled ~0.7C for 14
months; globally -0.4 C for the summer 1992).
El Chichon (1982) 0.6 km3 plinian, 10 Mtons SO2 , coincided with El Nino damping 0.5C NH cooling effects.
Agung (1963) 0.5 km3 subplinian, 20 Mtons SO2 , ~15-20 km column height, 0.3C NH cooling.
Krakatau (1883) >10 km3, ~50 Mtons SO2 , 40 km column height, 0.3C NH cooling.
Cosiguina (Nicaragua, Jan 1835) VEI=5 eruption; 1837 coldest year in N America in last 250 years.
Tambora (1815), 200 Mtons SO2 , 150km3 ash up to 50 km into the atmosphere, ~0.5-1C global cooling;1-2.5 C in
Europe, year without a summer, typhus epidemic, famine, plague.
Laki (1783) 0.3 km3 plinian, 12 km3 lavas, ~90 Mtons SO2 , ~1C NH cooling; European dry fogs.
Toba (~73,500 yrs ago) 2,800 km3 erupted ash >1,000Mton aerosols in atmosphere for ~6 years, 5-10 C cooling,
killed forests, coincided with onset of the last Ice Age; largest explosive eruption of the last few 100,000 yrs.
Ambrose (1998) suggested the Toba caldera eruption produced a human population bottleneck.
~1 every 50 years =Rate of major eruptions recorded in polar ice cores during the last 600 years (VEI=4-6) (Roscoe, 2001).
Using N hemisphere tree ring data from 380 sites,
Briffa et al (1998) found that the coldest summers during the last 600 years followed 10 major volcanic eruptions (VEI>6):
1452 Kuwae,Vanuatu; 1580 Billy Mitchell, Bougainville; 1600 Huaynaputina, Peru; 1641 Parker, Philippines, 1660 Long Island,
New Guinea; 1815 Tambora, 1883 Krakatau, 1902 Santa Maria, Guatemala; 1912 Katmai, AK; 1991 Pinatubo.
TOMS (Total Ozone Mapping Spectrometer) and other satellite instruments can detect volcanic emissions.
Selected references
Ambrose, S (1998) Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans J Human Evol.34, 623
Briffa et al (1998) Influence of volcanic eruptions on Northern Hemisphere summer temperature over the past 600 years Nature 393, 450
Robock, A (2000) Volcanic eruptions and climate Reviews Geophysics 38, 2, 191.
Roscoe HK (2001) The risk of large volcanic eruptions and the impact of this risk on future ozone depletion Natural Hazards 23 (2-3) 231.
Wohletz KH (2000) Were the Dark Ages triggered by volcano-related climate changes in the 6th century? EOS Trans. AGU 48(81), F1305
(http://www.ees1.lanl.gov/Wohletz/Krakatau.htm)