Creation 39(2):42–45, April 2017
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The puzzle of large natural bridges and freestanding arches
Large natural bridges and freestanding rock arches are structures left behind after erosive action, features called erosional remnants. Along with several other types of landforms examined in this magazine in recent years, they provide further evidence for rapid erosion in the late stages of Noah’s Flood.1
A natural bridge is an arch-like rock formation caused by erosion from running water, and typically spans a watercourse, which may now be dry. Three of the largest and most impressive natural bridges in the world are found in Natural Bridges National Monument, southeastern Utah, USA.2 Of these, the two associated with White and Armstrong Canyons were clearly eroded by water channeling down those canyons. Sipapu Natural Bridge, the largest of the three, is 67 m (220 ft) high and 82 m (270 ft) wide (fig. 1). Another impressive natural bridge in the southwest United States is Rainbow Bridge, near Lake Powell in northern Arizona.3
Freestanding rock arches
Although an arch looks similar to a natural bridge, it differs in that there is no obvious water course associated with it. Freestanding rock arches can be found on ridges or the sides of a ridge or mountain. The largest are high enough to contain the dome of the Capitol building in Washington D.C. Landscape Arch in Arches National Park, Utah, USA (fig. 2), is the second longest in the world, with a span of 88 m (290 ft). At the other end of the size scale, some arch configurations are little more than small holes in rock; in Bryce Canyon National Park these are called ‘windows’. Arches National Park, southeast Utah, has the greatest density of arches in the world—more than 2,000 of them, all different.4,5
Long-age geologists speculate that rock arches form slowly over long periods of time by: (1) uplift that causes deep vertical, parallel fractures to form; (2) weathering and erosion that enlarge fractures resulting in narrow vertical walls called ‘fins’; (3) continuing erosion with some fins breached from below; and (4) continued weathering that enlarges the holes, eventually causing the arch to collapse.6 They estimate that it would have taken 70,000 years for water, frost, and wind action operating in a dry climate to form the isolated Delicate Arch in Arches National Park (fig. 3).6
Small natural bridges and arches can form after the Flood
It is likely that most small natural bridges and arches formed in today’s climate after the Flood through erosion, especially since some of them are found in glaciated areas.7,8 Since they would be unlikely to survive glaciation, they must have formed after the post-Flood Ice Age. The windows in Bryce Canyon National Park are obviously a result of uneven weathering and erosion of the mostly soft rock. The mechanisms generally suggested for the formation of small natural bridges and arches are reasonable ones in a post-Flood erosion scenario.
Kolob Arch in northwest Zion National Park, Utah, USA, is typical of a large rock arch that likely formed after the Flood, probably from erosion at the base of a cliff, forming a depression, which was eroded further and separated itself from the cliff face.9,10 It is the third largest arch in the world, spanning 87 m (287 ft). This arch is now separated from the cliff by only 13 m (44 ft). It is not freestanding like Landscape or Delicate Arches, both of which are in Arches National Park.
Assumed uniformitarian origin not observed
The origin of arches and large natural bridges is problematic for uniformitarian11 science. Many hypotheses have been suggested,12 but all depend upon slow processes of erosion over tens of thousands of years. The problem with this much time is that the large natural bridges and arches would have weathered and collapsed long before the material around them eroded. Geomorphologist C.H. Crickmay noted that for large natural bridges to form, its erosion rate compared to the stream channel has to be almost non-existent, which makes no sense when considering that a natural bridge in its beginning stage will erode fast by rock fall.
“What is remarkable about its [natural bridge] history is that, in all the time required for the stream currents to corrode downward and laterally through a vertical depth of from 10 to 12 or 60 m [33 to 40 or 200 ft] in resistant rock, the progress made by ‘denudation’ [total erosion] toward destroying the fragile-looking bridge appears to have been virtually nil—a discrepancy in rates of action that may exceed 100,000 to 1 (emphasis mine).”13
Such a discrepancy in erosion implies large natural bridges were not formed slowly over a long time, but rapidly not that long ago.
Cruikshank and Aydin hypothesized that the majority of arches are caused by local enhancement of erosion by fracture concentration.5 Such an ‘obvious mechanism’ was supposedly missed by previous investigators. Unfortunately, no one has seen a large freestanding arch form by this mechanism. Arches are simply assumed to form by more rapid weathering at the base of a vertical slab of sandstone,14 but such differential erosion and arch formation is pure speculation:
Arch formation cannot be due solely to weathering and erosion, however, because these processes are not restricted to the sites of arches in rock fins. There must be some factor that locally enhances the effects of erosion within a rather small part of a rock fin to produce an arch. How erosion is localized within a rock fin to form an arch is enigmatic.15
Moreover, arches are rather rare, and if any of the uniformitarian mechanisms applied, there should be many more of them. Cruikshank and Aydin summarized:
There is no need to invoke reasons such as weak cement, unloading, or exfoliation to explain the presence of arches, especially when these processes act on similar rocks in nearby regions without producing the same abundance of arches.16
A new hypothesis suggests that erosion near the base of a fin starts because of water trapped above an impervious barrier. This causes stress changes above, which creates a more stable, tough structure that resists weathering.12,17 Eventually, the erosion at the base works its way through to form an arch. Although this mechanism seems plausible, it requires angular sand grains to lock together for greater strength. Practically all the arches in Arches National Park are made of homogenous sandstone in which the sand grains are rounded, with no lower impervious layer.
Despite all the hypotheses, an important point has been neglected. Science depends upon observation, and we observe the destruction of large freestanding arches and natural bridges, but never their formation. For instance, portions of Landscape Arch in Arches National Park have collapsed since the 1940s. One of the most photographed freestanding arches in Arches National Park was Wall Arch (fig. 4). However, it collapsed during the night of 4–5 August 2008 (fig. 5).
A possible late Flood mechanism
Large freestanding arches and natural bridges on the continents are delicate features that seem impossible to form in the present climate, considering only 4,500 years have passed since the Flood. The best explanation is they were formed by quick erosion, possibly late in the run-off phase of the Flood. Large natural bridges imply rapid erosion. They could have been formed during the Channelized Flow Phase of the Flood when the canyon was cut. The last vestiges of Flood erosion would have created the conditions where the formation of those magnificent (and otherwise so enigmatic) structures, freestanding arches, became possible due to differential erosion in that particular location.
References and notes
- Oard, M.J., Many arches and natural bridges likely from the Flood, J. Creation 23(1):115–118, 2009.
- The three bridges are Kachina, Owachomo, and Sipapu. Return to text.
- Huntoon, J.E. et al., Geology of Natural Bridges National Monument, Utah; in: Sprinkel, D.A., et al., Geology of Utah’s Parks and Monuments, Utah Geological Association Publication 28, 2nd edn, Salt Lake City, UT, pp. 232–249, 2003. Return to text.
- Harris, A.G. et al., Geology of National Parks, 5th edn, Kendall/Hunt Publishing Co, Dubuque, IA, pp. 80–91, 1990. Return to text.
- Cruikshank, K.M., and Aydin, A., Role of fracture localization in arch formation, Arches National Park, UT, Geol. Soc. Am. Bull. 106(7):879–891, 1994. Return to text.
- Harris et al., Ref. 4, p. 83. Return to text.
- Cleland, H.F., North American natural bridges, with a discussion on their origin, Geol. Soc. Am. Bull. 21(1):313–338, 1910. Return to text.
- Wentworth, C.K., Natural bridges and glaciation, Am. J. Sci. 26 (156):577–584, 1933. Return to text.
- Manning, A., Arches and natural bridges, J. Creation 23(2):67–68, 2009. Return to text.
- Oard, M.J., Arches and natural bridges: Michael Oard replies, J. Creation 23(2):68, 2009. Return to text.
- Uniformitarianism = the belief that most geology must be explained by the sorts of processes operating today over vast timespans. Return to text.
- Bruthans, J. et al., Sandstone landforms shaped by negative feedback between stress and erosion, Nat. Geosci. 7:597–601, 2014. Return to text.
- Crickmay, C.H., Discovering a meaning in scenery, Geol. Mag. 109(2):172, 1972. Return to text.
- Harris et al., Ref. 4, pp. 81–83. Return to text.
- Cruikshank and Aydin, Ref. 5, p. 879. Return to text.
- Cruikshank and Aydin, Ref. 5, p. 891. Return to text.
- Paola, C., Emergent sculpture, Nat. Geosci. 7:552–553, 2014. Return to text.
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