Mathematics – Logic
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.v23b..05p&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #V23B-05
Mathematics
Logic
1030 Geochemical Cycles (0330), 1223 Ocean/Earth/Atmosphere Interactions (3339), 8164 Stresses: Crust And Lithosphere, 8450 Planetary Volcanism (5480)
Scientific paper
Global rates of occurrence of volcanic eruptions show periodic behaviour on timescales ranging from <1 yr (seasonal) to >106 years. At long timescales (>106 to 107 years), rates of eruption are controlled by plate tectonics. At shorter timescales, the periodic nature of volcanism is forced by the global water cycle. Historical records of the rates of onset of eruption for the past 300 years are dominated by small-scale activity at a number of persistently, or repeatedly, active volcanoes around the world. This record shows statistically significant evidence for `seasonality': globally, rates of eruption are about 18% higher during northern hemisphere winter than northern hemisphere summer. This pattern of seasonality is strong for volcanoes at high northern latitudes; but also exists for volcanic regions in the southern hemisphere (e.g. Chile) and at specific volcanoes (e.g. Sakurajima, Japan). Seasonality is weak at certain ocean-island volcanoes (e.g. Hawaii), and certain volcanic regions (e.g. Mediterranean). The only external parameters that account for the periodic nature of small-scale volcanism (i.e. the observation that eruption rates peak between November and March in both hemispheres) are those related to the global water cycle. Movement of water (including atmospheric vapour; soil moisture; snow and ice) between the northern-hemisphere continents and the world's oceans is responsible for an annual deformation of Earth's surface that is weakly defined in equatorial regions, and stronger at higher latitudes. This external modulation of the Earth's surface has an amplitude of the order of centimetres, and an associated (vertical) strain rate of ~ 10-16 s-1. This deformation is slow enough to be felt by the Earth's interior, and is of the same order of magnitude as the (horizontal) strain rates experienced in tectonically active continental regions. This modulation effectively applies a time-dependence to the `threshold' point at which a volcano will begin to erupt. In this way, the subtle, small-magnitude but long-wavelength changes associated with the annual hydrological cycle leads to clustering of volcanic eruptions. Peaks of eruption onset are associated with periods of changing sea-level or atmospheric pressure, rather than with the maxima or minima. Longer timescale (> 103 year) variability in rates of volcanism during the Pleistocene, associated with large scale climatic changes, is evident in long-term terrestrial and ice-core records of volcanism. Linkage between the global hydrological cycle and volcanism over annual to millennial timescales plays an important role in land-atmosphere coupling by modulating volcanic emissions and, thereby, the volcanic component of climate forcing.
Dade W. B.
Jupp Tim E.
Mason B. G.
Pyle David M.
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