Magnetoclimatology: a test of the wind-vigour model using the 1980 Mount St. Helens ash

Magnetic mineralogy is now commonly employed in the study of past climate changes, but the underlying magnetoclimatological mechanisms are not fully understood. Many important instances have been reported where pedogenesis leads to magnetic enhancement; warmer, more humid conditions produce higher magnetic signals. However, significant exceptions occur, wherein colder, more arid conditions lead to higher magnetic content. One suggested explanation for the latter is the so-called wind-vigour model in which glacial intervals are associated with stronger, more frequent winds which are more efficient at entraining and transporting dense iron oxide particles. This notion is tested here by determining the relevant magnetic properties of the ash produced by the 1980 eruption of Mount St. Helens. A clear exponential decrease of magnetic susceptibility with increasing distance from the vent is observed. This supports the wind-vigour concept (at least in some environments) as a viable alternative to the pedogenetic model of magnetoclimatology.