IN A FEW WORDS

Origins 10(1):3 (1983).

Brief summaries of the main conclusions of the leading presentations are given below for those who may find the complete articles too long or technical.

MOUNT ST. HELENS AND SPIRIT LAKE

    The eruption of Mount St. Helens has become a unique opportunity to study rapid geologic activity. Miles of forests were blasted down, giant slides and debris flows changed the topography of the Toutle River Valley, and new lakes were formed. At the base of the mountain, a larger Spirit Lake now supports a huge log raft. Some of the logs are floating erect or are sitting upright on the bottom. Some past geologic phenomena such as the series of petrified forests of Yellowstone may be explained in part by the study of this eruption and its associated activities.

PALEOMAGNETISM I

    When molten rock from a volcano cools or when sedimentary rocks are formed, the magnetic particles in each align themselves according to the prevailing magnetic field of the earth. Igneous rocks are the most magnetic and sedimentary the least, but both have sufficient magnetic minerals to be useful in studying the past history of the earth's magnetic field. The correct determination of the direction and intensity of the ancient magnetic field is affected by the various ways a rock can become magnetized as well as by alteration of the original rock magnetism with time.
    If the shape and orientation of the earth's magnetic field in the past can be assumed to be similar to the present, then it is possible to predict the original magnetic latitude and orientation of a magnetized rock. This type of information has been used extensively in the development of the theory of plate tectonics. Paleomagnetism also gives strong evidence of "reversals" of the earth's magnetic field. Did these reversals of the earth's magnetic field, in fact, occur? Have the plates really moved about on the surface of the earth? If so, then what are the implications for the tectonic history and age of the earth?
    In this series of two articles the author hopes to provide the reader with sufficient background information that he can, with some understanding, appreciate the applications and implications of this fascinating area of geophysics for the study of earth history.