Tuesday, August 19, 2014

Rapid erosion of a gorge in Taiwan

The Daan River bedrock gorge in Taiwan.
Credit: Kristen Cook.  Image source.
My eye was caught by an article recently that proclaimed that a new study shows how erosion can happen much faster than normal.  Naturally, such a claim is of interest to young-earth creationists, as we work with a much shorter timeline of history than do most geologists.

The geologists involved in the study investigated the formation and subsequent erosion of a gorge in Taiwan through which the Daan River flows.  Interestingly, the paper does not focus on the formation of the gorge, but rather on its transition back to a flat plain.  The gorge was documented as forming after the river breached a natural dam in 2004.  Within four years, a gorge a kilometer long, 25 meters wide, and 17 meters deep had been carved out by the water.  Normally, the water would continue to flow through the gorge and slowly erode the bottom and sides.  In this case, however, the river takes a sharp turn before entering the gorge, which causes the sediment-rich water to violently abrade the outer edge of the turn, eroding it very quickly.  The scientists estimate that the gorge will disappear within 50 to 100 years.

This overall eroding action is termed "downstream sweep erosion" by the authors, referring to the widening of the gorge from the sharp turn propagating downstream.  The actual mechanism of erosion is not a new discovery, just the geometric/geographic context.  The ability of water to erode great amounts of rock in short periods of time is well-known among geologists and well-documented in this case.  Unfortunately, the perception of the public still appears to be that water takes millions of years to form large canyon-like structures, regardless of the amount or velocity of water.  This appears to be a side-effect of the uniformitarian proclamation that "rates are constant" in nature.  It might be more accurate to say that rates are mathematically predictable rather than constant.  The eroding rate of water is greatly dependent on the volume of water, the velocity of water, the sediment content of the water, the direction and type of flow, and the type of rock being eroded.  This means that a stream of constant velocity, constant direction, consistent flow type, constant volume, and constant sediment load will erode a uniform bed of rock at a constant rate.  However, you cannot assume that this stream will have a similar erosion rate to another stream with differing attributes.  In fact, it is highly likely that they will have different rates.

While I will not suggest that the Grand Canyon was formed within a few years after the Flood by downstream sweep erosion specifically, the implication is simply that one cannot use the current erosion rate of the Colorado River to extrapolate to the beginning of its formation.  This goes for many geologic features, not just the Grand Canyon.  Many people suggest that the young-earth timeline does not allow for enough time for the erosion of the Rocky or Appalachian Mountains from their initial uplifted stage, but time is only an issue if a constant rate is assumed.  If the volume of water and other erosive forces was not constant, then neither was the erosion rate.  The biblical Flood of Noah's day would be a sufficient departure from "normal" to account for such accelerated rates.  Can I scientifically prove that Noah's Flood occurred as described in the Bible?  Probably not, but I maintain that it is consistent with the observed evidence.

No comments:

Post a Comment