This article is from
Journal of Creation 34(1):3–4, April 2020

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Complex water gap features—Krichauff Range, Northern Territory, Australia

by Ron Neller

 

The term water gap, or transverse drainage, refers to a river that cuts through a mountain range as though it was not there. Although they are often pictured as narrow gorges, they are in essence a pass through a mountain ridge cut by a river and through which a river still flows. Frequently cited examples of such features include the Grand Canyon,¹ Hells Canyon in Oregon,² Himalayan rivers such as the Arun River of Nepal,³ ranges across north and north-east Iraq,⁴ and the Finke and Todd Rivers in Northern Territory, Australia.^5,6 This short paper outlines unusual water gap features in the Krichauff Range in central Australia that need further research.

Current water gap thinking

There has been minimal geomorphic and geologic research on the origin of water gaps. Within the secular earth science literature, rivers that produce these landscapes have been primarily classified as either antecedent or superimposed rivers, or a combination of both (anteposition).⁷ Antecedent rivers are those believed to be the older component of the landscape, maintaining a course that precedes the emergence of the rising terrain. In this case the rate of river erosion exceeds that of the rate of uplift of the land. On the other hand, superimposed rivers are those that erode down from a higher surface but retain their course regardless of the different strata they encounter.

In addition to these two arguments, a more recent article⁸ outlined a criteria-based methodology for determining the mechanism of water gap development, and strongly promoted two other processes. These include river piracy, when a river captures part of another river’s catchment through headwater erosion, and overflow, when a lake breaches surrounding terrain and creates a new river.

Given that current classifications are based on interpretations of past landscapes and events, which are no longer evident or occurring, distinguishing the processes believed to form water gaps or their features is fraught with uncertainty—not the least of which is the lack of physical evidence that would suggest one process over another. As one author⁷ notes: “In theory the concepts are quite simple but in practice it is often difficult to distinguish superimposition from antecedence”, and he warns of the danger of “inventing surfaces that never existed”.

Water gap channel patterns

Water gap valleys often wind irregularly, though on occasion take on a more systematic spiral course (becoming highly sinuous). While water gaps give passage to rivers, they at the same time often constrain them. This is frequently recognized in research papers using words such as ‘maintain’ and ‘imposed’. Indeed, as just outlined, most water gap publications argue that the constrained river meanders are historic features: a component of a palaeovalley. This is regardless of whether the water gap was classified as antecedent, superimposed, river piracy, or overflow in origin.

Because water gaps largely constrain rivers flowing through them, they rarely exhibit elongation of their river axis, significant lateral erosion, migration of meander loops, or cutoff events that are more classically associated with meandering channels on alluvial floodplains.⁹

Finke River and Ellery Creek features in the Krichauff Range, Australia

In a recent cursory examination of Australian water gaps, some minor but unusual morphological features were observed along the Finke River and Ellery Creek water gaps, particularly within the semi-arid Krichauff Range in central Australia south of Hermannsburg.

The Krichauff Range essentially consists of folded sedimentary rocks known as the Hermannsburg Sandstone, comprising red-brown sandstone, pebbly sandstone, and minor silty sandstone. While it is a region of varying relief, the ridges are characteristically 200–300 m above the valley floors.

Based on previous research the Finke River has been publicly proclaimed as possibly the oldest river in Australia. The largely sedimentary deposits that comprise the Krichauff Range are believed to have been uplifted around 300 million years ago. The water gaps are also believed to be considerably old. For instance, in an interview the Director of the Northern Territory Geological Survey states that “the Finke has followed exactly the same course for the past 15 to 20 million years”.¹⁰ This is perhaps argued because the Finke exhibits deeply incised and sinuous meander bends through the range. A tributary of the Finke River, Ellery Creek, also flows through multiple water gaps.

However, Finke River and Ellery Creek, passing through many water gaps in their journeys, are better explained by Noah’s Flood rather than other ideas proposed.¹¹ In both catchments the rivers have developed water gap valleys through diverse topographic and geologic settings.

For instance, Finke River and Ellery Creek have each created two pathways at the base of their valleys in the Krichauff Range, one contemporary and one abandoned (figure 1). For each system, both channels are found within a larger water gap valley. Moreover, in both instances the contemporary and the abandoned channels in these systems intersect frequently, their paths crossing over at least 10 times along the Finke River and at least five times along Ellery Creek.

Furthermore, a closer examination of these systems using Google Earth Pro shows that hills (sedimentary rock structures) exist between the contemporary and the abandoned channels in each system. These are usually over 30 m and up to 59 m in height between the contemporary and abandoned channels of the Finke River, and as low as 15 m (where the gaps are a minor distance apart) and up to 63 m in height between the contemporary and abandoned channels of Ellery Creek. This clearly eliminates any thought that the abandoned channels were formed by river channel migration across a floodplain that create ‘oxbows’ or abandoned channels.

Thus, both the Finke River and Ellery Creek have carved current and previous channels within the broader water gap valleys, such that these channels regularly intersect. For each valley there is a clear ‘active’ channel and an ‘abandoned’ channel. Indeed, this is not the only example of such complexity, as a quick overview using Google Earth Pro reveals a similar pattern on the Hugh River 55 km to the east.

Since the contemporary and abandoned channels are intertwined (crossing each other’s path regularly), within these two catchments the antecedent and superimposed models of formation are redundant. Rivers are unable to rise over a host of hills and develop new channels adjacent to, and intersecting with, the original channels. Piracy is also removed as there is no evidence of one river system capturing the headwaters of another. The final explanation, of a past lake breaching the surrounding terrain, is also inadequate. After all, there is not one water gap valley, but two. Past lake breaches would need to have occurred in both catchments.

Further research needed

Further research on these unique channel features may facilitate a deeper understanding of water gap formation in the Recessive stage of Noah’s Flood. For example, these features could have been developed in the following manners:

1. The water gaps may have housed an anastomosing flow pattern (two interconnected channels that capture a flood basin’s activity, especially in low-energy conditions approaching base level) during the latter stages of the Flood. As the Flood’s erosive energy declined, then lower valley relief irregularities may have been retained, leading for a short period to multiple active channels.
2. Due to continuing upstream landscape changes there may have been a significant fluctuation in the volume of the receding Flood—perhaps a short-period increase leading to the formation of an entirely new channel and the abandonment of that already formed.

Other suggestions associated with changes in base level may also need exploring.