Debates in Science - 2

The material for this post has essentially been taken from J Harlen Bretz And the Great Scabland Debate by Sean D. Pitman.

(I apologise for taking material without permission but I am doing it only because they help me to make a point that otherwise would be difficult)

The concluding comments have been taken from Wikipedia.

(... Continued from the previous blogpost.)


        It was only around 1940 that things began to slowly change for Bretz. At the American Association for the Advancement of Science in Seattle Washington, many papers were presented in a session entitled, Quaternary Geology of the Pacific, which strongly supported a non-catastrophic origin for the channelled scablands.
 
  Finally, Pardee, the eighth speaker of the session, spoke benignly about the "Ripple Marks in Glacial Lake Missoula."  In a low key manner Pardee described the huge "ripple marks"  with heights of up to 15 meters and spacings of as much as 150 meters, as due to flooding, as well as his old theory that Lake Missoula was the source of the water that obviously created the unusual current beds found in the Montana prairie region. He went on to suggest that about 2,000 cubic km of water were held in the lake and that the evidence showed that a glacial dam had once blocked off the mouth of this lake. He presented convincing evidence, to include severely scoured constrictions in the lake basin, huge bars of current-transported debris, and giant current ripple marks, which all strongly suggested that the ice dam had been breached in a very dramatic fashion. Pardee went on to propose that the way this occurred was that the ice dam had blocked the water until the water became deep enough to lift up the ice dam and allow the blocked water to rush out with almost unimaginable force so that the lake was completely emptied within just 48 hours. He suggested that the lobe of the Cordilleran Glacier was the actual plug or dam that blocked the Clark Fork River. This ice dam caused the formation of Lake Missoula (4,150 feet above sea level) to reach a depth of about 2,000 feet over some 3,000 square miles. When the ice dam failed, 500 cubic miles of water rushed out of Lake Missoula at 50 to 60 miles per hour (or 9.46 cubic miles per hour), which translates into a 2,000 foot wall of water smashing with Herculean force all the way to the pacific ocean.

Today it is believed that this huge flood of water rushed across Idaho's northern Rathdrum Prairie and into eastern Washington where it divided into three huge flows, each up to 600 feet deep traveling at 45 miles per hour.  To understand a bit of this magnitude, this flow was ten times more massive than the flow of all the rivers in the entire world today. As this flood raged across the Spokane Valley and out across the loess-covered basalt plateau, it carved out the 20-mile-wide Cheney-Palouse Tract, the 14-mile-wide Crab Creek Channel, and the 50-mile-long Grand Coulee as well as numerous cross or "braided" channels.

Pardee's evidence for the origin of massive amounts of flood waters was, of course, just what Bretz needed. This evidence was just enough proof for Bretz to confirm the source for and cause of the watery cataclysm that he knew must be there somewhere. All the rest fell into place since all the information to back up the effects of such a cataclysm had already been ready and waiting for many years.

 In 1952 Bretz made yet another field trip to the scablands and returned with even more evidence to include detailed maps, aerial photographs, and sedimentological information. In his subsequent 1956 paper, Bretz concluded that the most convincing evidence for a cataclysmic flood proved to be the presence of giant current ripples on bar surfaces. These ripples clearly showed that bars up to 30 meters high were completely inundated by phenomenal flows of water. Numerous examples of giant current ripples were found on the same bars that Flint had interpreted as normal river terraces. As it turns out, Pardee's recognition of the giant current ripples of Lake Missoula was followed by Bretz's documentation of 15 more scabland ripple fields and then by Baker's and Nummedal's identification of 100 more rippled areas. Such features could only have been produced by the flow of very deep water at velocities of truly enormous catastrophic proportions. This was the beginning of early acceptance and painful recognition of the validity of Bretz's position by geologists.

Bretz's remarkable work was built painstakingly over many years, but he had to fight great opposition for many decades for its final acceptance. Finally, in 1979, the geological establishment publicly acknowledged Bretz's work by awarding him the prestigious Penrose Medal - the most prestigious honor in the field of geology. Bretz was in his late 90s, and had been holding the line for more than 50 years before finally realizing general acceptance of his "insane" catastrophic model for the formation of the Channeled Scablands of eastern Washington State.

Uniformitarianism was originally proposed in contrast to catastrophism, which states that the distant past "consisted of epochs of paroxysmal and catastrophic action interposed between periods of comparative tranquility"   Especially in the late 19th and early 20th centuries, most geologists took this interpretation to mean that catastrophic events are not at all important in geologic time.  An important result of the Scabland debate discussed above and others was the re-clarification that, while the same principles operate in geologic time, catastrophic events that are infrequent on human time-scales can have important consequences in geologic history.  Derek Ager has noted that “geologists do not deny uniformitarianism in its true sense, that is to say, of interpreting the past by means of the processes that are seen going on at the present day, so long as we remember that the periodic catastrophe is one of those processes. Those periodic catastrophes make more showing in the stratigraphical record than we have hitherto assumed.”


Even Charles Lyell thought that ordinary geological processes would cause Niagara Falls to move upstream to Lake Erie within 10,000 years, leading to catastrophic flooding of a large part of North America.


Unlike Lyell, modern geologists unfortunately do not apply uniformitarianism in the same way. They question if rates of processes were uniform through time and only those values measured during the history of geology are to be accepted.  "The present may not be a long enough key to penetrate the deep lock of the past"  (Ager, Derek V., 1993). Geologic processes may have been active at different rates in the past that humans have not observed. “By force of popularity, uniformity of rate has persisted to our present day. For more than a century, Lyell’s rhetoric conflating axiom with hypotheses has descended in unmodified form. Many geologists have been stifled by the belief that proper methodology includes an a priori commitment to gradual change, and by a preference for explaining large-scale phenomena as the concatenation of innumerable tiny changes.”


The current consensus is that Earth's history is a slow, gradual process punctuated by occasional natural catastrophic events that have affected Earth and its inhabitants. In practice it is reduced from Lyell's conflation to simply the two philosophical assumptions. This is also known as the principle of geological actualism, which states that all past geological action was like all present geological action.