CATASTROPHIC FLOODING: A CASE STUDY IN THE VALUE OF OUTRAGEOUS GEOLOGICAL HYPOTHESES

One hundred years ago, in the summer of 1922, Professor J Harlen Bretz (1882-1981) took his Univ. Chicago summer advanced field course graduate students into a new area: the Channeled Scabland of Washington state. They documented a landscape that seemed different than any other, and Bretz formulated the outrageous geological hypothesis that it had formed through cataclysmic flooding. This outrage was imposed on what many considered to be the principle that had made geology into a respectable science: uniformitarianism. Long earlier, the logical flaws in this doctrine had clearly been stated by William Whewell (1794-1866), the originator of the term. But nearly all practicing geologists so adhered to the lawyerly arguments made Charles Lyell in his book Principles of Geology that they viewed as unscientific any catastrophic explanations for Earth phenomena.

Shortly after Bretz’s discovery, in 1925 William Morris Davis (1850-1934) presented an address at Univ. California on “The Value of Outrageous Geological Hypotheses” advocating, as a cure for “theoretical stagnation,” that, “violence must be done to many of our accepted principles.” In the published version of that talk (Science, v. 63, no. 1636, p. 463-468, 1928) Davis states that an outrageous hypothesis for some geological behavior serves as a stimulus to geological thinking by encouraging, “contemplation deliberate enough to seek out just what conditions would make the outrage seem permissible and reasonable, ” while also, “encouraging the contemplation of other possible behaviors.”

It took decades of controversy before the Bretz hypothesis finally prevailed against its critics. What followed over the past 50 years was the discovery and documentation of ancient cataclysmic megaflood landscapes throughout the world and even multi-billion-year-old evidence of megaflooding on Mars. Discoveries made through megaflood studies were applied to rare, high-magnitude Holocene and Anthropocene flood phenomena, resulting in a new science that was named “paleoflood hydrology.” Combining geological modes of inference with conventional engineering methods of flood analysis, paleoflood hydrology extrapolates from geological evidence of extreme, rare floods to estimate the risk for the more common floods that pose maximum hazard to humans and their works.