London Bridge has fallen down
In January 1990 a span of London Bridge collapsed, so its name was changed to London Arch. The arch is a tourist attraction along the Great Ocean Road near Port Campbell in Victoria, Australia. Before the collapse, visitors were able to walk from the mainland across the double-span natural bridge. Oceanic erosion of the limestone coastal cliffs caused the formation of the bridge and also caused its collapse to form an arch. Eventually arches collapse to form stacks like The Twelve Apostles, which are icons of the Australian landscape in the vicinity of London Arch (Appendix A).
In this post we will see that rock coastlines are eroding faster than we think.
When walking along the coastline north of Sydney, I noticed the rock platforms at Terrigal and Avoca. According to Google maps these rock platforms could be up to about 60-80m and 50-80m wide. But lidar measurements show that the rock platform at Avoca is up to about 40-50m wide. As there was a cliff collapse (rock fall) at the Terrigal Skillion in July 2018, the cliffs associated with these rock platforms still seem to be undergoing erosion due to wave action. I wondered how long it would take to erode a rock platform of this width. The sedimentary rock forming The Skillion (known as the Terrigal Formation) is classified as Middle Triassic and is overlain by Hawkesbury sandstone. A newspaper article stated that “The unstable nature of the site is likely to continue as waves slowly erode and undermine the cliff”.
A study found that the mean widths of coastal rock platforms in central-southern NSW (Laker 2016) were:
– 45m (ranging 15-130m) in the Central Coast
– 25m (ranging 15-45m) in the Sydney region
– 55m (ranging 20-105m) in the Illawarra region.
The rocks at these locations are mainly sandstone. For example, at Avoca it is “interbedded laminate, shale, fine-to coarse-grained quartz to-quartz-lithic sandstone and minor red claystone”.
The two main explanations of the earth’s geological history (Biblical and Uniformitarian) are described in Appendix B. According to the uniformitarian time scale, the sea level rose after the last ice age to reach its current level about 7,000 years ago (Table 2). Whereas, according to the biblical time scale, the sea level rose after the ice age to reach its current level about 3,800 years ago, which is 54% of the uniformitarian value (Walker, 2015). If we assume that the rock platforms were eroded over these time periods (3,800 years for the biblical explanation and 7,000 years for the uniformitarian explanation), we can calculate a mean rate of erosion of the coastal cliff for each time scale (see Table 1).
Table 1. Inferred mean cliff retreat rates for rock platforms of various widths according to the Biblical and uniformitarian time scales.
|Rock platform width (m)||Mean rate of coastal cliff erosion (cm/yr)|
So the mean rate of coastal cliff erosion for Avoca rock platform of 40m is calculated to be 0.6 cm/yr under the uniformitarian time scale and 1.1 cm/yr under the biblical time scale. And the mean rate of coastal cliff erosion for the widest rock platform in central-southern NSW of 130m is calculated to be 1.9 cm/yr under the uniformitarian time scale and 3.4 cm/yr under the biblical time scale.
But how do these inferred cliff retreat rates compare with actual cliff retreat rates?
Cliff retreat rates
An international review of the erosion of rocky coastal cliffs found median erosion rates of 3 cm/yr for hard rocks, 10 cm/yr for medium rocks and 23 cm/yr for weak rocks (Premaillon et al., 2018). The hard (resistant) rocks were granite, basalt, gneiss or limestone. The medium resistant rocks were claystone, shales or siltstones. And the weakly resistant rocks were mainly poorly consolidated rocks (weakly cemented sandstones, glacial tills and glacial sands) or chalk or strongly weathered rocks. The most commonly used measurement method was the comparison of aerial photographs or historic maps, which allowed for erosion evaluation spanning several decades. Coastal cliff erosion was primarily driven by cliff settings (type, weathering, folding, faulting, bedding) with less impact from marine forcing (swell, tidal range) and continental forcing (rainfall, frost, groundwater).
And the range of measured cliff retreat rates in the UK was 2-50 cm/yr (Earlie, 2015).
Based on measurements obtained using comparisons of Ordnance Survey maps between 1892 and 1960, the rate of retreat of the cliffs at Staithes (England) is estimated to have been 5 cm/yr (Agar, 1960). This rate has been averaged from a calculated rate of 4cm/yr for coastal headlands and 7 cm/yr for embayments.
The annual cliff retreat over a period of 7 years for cliffs on the UK North Sea coast comprised of shales, limestones, siltstones, and mudstones, all capped with sandstone was 3 cm/yr (Rosser et al., 2013). These cliffs were up to 60 m high in the North York Moors National Park.
California coastal cliff erosion rates were found to be 3 cm/yr for sandstone cliffs and 10-30 cm/yr for weaker sedimentary rocks (Griggs and Patsch, 2004).
There are other examples in the literature with higher erosion rates for coastal rocky cliffs.
When researching coastal cliff retreat rates it’s important to check the method being used to see if they are actual rates or inferred rates. For example, shore platform widths and the uniformitarian timescale have been used to estimate mean cliff retreat rates (de Lange and Moon, 2008). These are inferred cliff retreat rates (like those in Table 1) and not actual cliff retreat rates.
In August 2019 three people were killed when a sandstone cliff collapsed at a beach in Encinitas, north of San Diego. The collapse near Grandview Beach was blamed on natural erosion. There were signs posted at the beach warning people to stay back from the unstable bluffs. This erosion is usually slow and gradual, but sometimes occurs in major bluff failures or collapses. Being caught in a bluff collapse area can cause serious injury or death, a beach safety guide said.
The uniformitarian explanation proposes multiple ice ages over millions of years. This is based on indirect observational methods (like erosional or depositional features). For example, the Cryogenian ice age (635-720 millions of years BP) was proposed to explain geological evidence for the apparent presence of glaciers at tropical latitudes. However, many “glacial” features can also be created by non-glacial means such as avalanches. As uniformitarians are more likely to attribute these to an ice age rather than a sudden tectonic uplift or a global flood, whenever they see these erosional or depositional features they claim it was an ice age. I wonder how many of these erosional or depositional features could be caused by avalanches? Because of this, I suggest that the number of ice ages is overstated in the uniformitarian explanation.
Uniformitarians also use indirect means to estimate the sea level in ancient times. For example, they measure parameters such as the concentrations of oxygen isotopes (δ18O) in benthic foraminifera and plankton and use various assumptions to estimate the global ice volume. From this calculation, they estimate the global sea level. As all these assumptions are based on uniformity and the geologic time scale, they are invalid if there was a global flood. This means that the estimated sea level fluctuations over millions of years made by such indirect methods probably bear little resemblance to the actual sea levels.
The ice age
Measurements of the depth of the sea bed near continents indicate that during the ice age the sea level was lower than it is today. During the ice age, the “continental shelf” around the continents was above sea level. For example, sea bed mapping of the continental margin of Australia (Harris et al, 2005) showed that the “shelf-break” (the outer boundary of the continental shelf) is currently at the following depths:
– 70-165m in Eastern Australia, and 80-110m in northern NSW, and 130-170m beneath sea level in central and southern NSW.
– 200m beneath sea level in South-Eastern Australia
– 125-170m beneath sea level in Southern Australia
– 110-150m beneath sea level in Western Australia
– 120-150m beneath sea level in Northern Australia
So, the continental shelf around Australia is typically about 120-150m deep. This gives an approximation of the rise in sea level since the glacial maximum in the ice age (assuming that the continent has been tectonically stable since then, which seems to be true to within 5m; Bryant, 1992).
According to the uniformitarian timescale, the sea level rose over a period of about 10,000 years, whereas under the biblical timescale the time period is about 200 years. Thus according to the uniformitarian time scale the sea rose at about 3 m per century, whereas according to the biblical timescale it was more like 60m per century.
It is estimated that during the peak of the ice age atmospheric temperatures were about 7 deg C cooler than today. After this, according to the uniformitarian timescale, the temperature increased for 6k years to reach current levels and it has been constant for the past 12k years. Whereas, under the biblical timescale the temperature increased for about 200 years to reach current levels and it has been constant for the past 3.8k years. Thus according to the uniformitarian time scale, after the peak of the ice age the temperature rose at about 0.1 Deg C per century, whereas according to the biblical timescale it was more like 3.5 Deg C per century.
The mean widths of the coastal rock platforms in central NSW were 25-55m, which represent coastal cliff retreat rates of 0.4-0.8 cm/yr under the uniformitarian time scale and 0.7-1.4 cm/yr under the biblical time scale. And the widest coastal rock platform was 130m, which represents a coastal cliff retreat rate of 1.9 cm/yr under the uniformitarian time scale and 3.4 cm/yr under the biblical time scale. These cliff retreat rates are generally lower that those reported in the literature; such as 3-4 cm/yr for hard rocks. And the rates are higher for softer rocks. The rocks in central NSW were mainly sandstone, which has a high-medium hardness (resistance). Studies have found that cliffs comprised of such rocks typically erode at 3-10 cm/yr (Premaillon et al., 2018). So calculations of coastal cliff retreat rates in New South Wales, Australia, show that the biblical time scale gives results closer to measured cliff retreat rates than the uniformitarian time scale. This indicates that the biblical time scale is more realistic than the uniformitarian one.
According to the biblical timescale, after the ice age the earth returned to the current sea levels and current temperatures much more rapidly than is estimated under the uniformitarian timescale. This means that the earth’s sea levels and temperatures have changed more rapidly than is assumed in the uniformitarian model.
It’s interesting to note that because of the lower sea levels during the ice age, there were land bridges between many land masses which would have assisted the migration of land animals across the earth after the flood and the migration of people across the earth from the city of Babel after they divided into different language groups.
The earth’s geological and fossil record is able to be interpreted in two different ways. According to the Biblical explanation it is a reminder of the death and judgment that occurred during the flood. According to the uniformitarian explanation it’s a reminder of the evolution of species, which is a creation story. Which is the best explanation? One of the reasons that I favor the Biblical one is the presence of fossils within sedimentary rocks. We don’t see creatures being fossilized today on the large scale that occurs in sedimentary rocks. And adding extra time (millions of years) doesn’t increase the likelihood of fossilization. Also, if evolution was true, there should be many fossils of transitional creatures, but this is not the case. The fossils can be identified as those of creatures that are still alive today or those of extinct species. In fact the fossil record shows more evidence of extinction than of creatures evolving from common ancestors.
The two main explanations of how water and ice have shaped our earth are the Biblical flood and uniformitarian processes. The former is a much more rapid process than the latter. The flood also provides a process for large-scale deposition, large-scale fossilization and large-scale erosion which uniformitarianism lacks.
Observations show that rock coastlines are eroding faster than is assumed under the uniformitarian time scale. Calculations of coastal cliff retreat rates in New South Wales, Australia, show that the biblical time scale gives results closer to measured cliff retreat rates than the uniformitarian time scale. This indicates that the biblical time scale is more realistic than the uniformitarian one. So with respect to coastal erosion, the biblical time scale is more realistic than the uniformitarian one. This means that coastal geomorphology provides another reason (besides fossilization of large animals and orally-transmitted Aboriginal stories) to be skeptical of the uniformitarian (geologic) time scale.
Appendix A: The twelve apostles
The Twelve Apostles is a collection of limestone stacks off the shore of Port Campbell National Park, by the Great Ocean Road in Victoria, Australia. The rock stacks that rise up majestically from the Southern Ocean on Victoria’s dramatic coastline were created by constant erosion of the limestone cliffs. They are similar to The Needles of the Isle of Wright.
When they were named the Twelve Apostles in the 1920s, there were only eight stacks in the cluster. That was reduced to seven following the dramatic collapse of one (45m tall) in July 2005. There is a smaller stack that is sometimes counted as one of the twelve apostles. In 2016, a further five limestone stacks were discovered underwater about 600m offshore and further westwards.
In 2009, Island Arch collapsed to become two stacks instead. Later that same year, one of the limestone rock stacks known as The Three Sisters also crashed down into the sea. And as mentioned above, one of the arches of London Bridge collapsed in 1990.
The erosion rate of the cliffs behind the Twelve Apostles has been measured at about 30 cm/yr (22cm/yr for 1947-1994 and 36cm/yr for 2004 to 2014 (Bezone et al, 2016). This is an example of rapid erosion.
It’s interesting to note that the white chalk cliffs of southern England seem to be eroding 10 times faster than is estimated using the uniformitarian time scale. Measurements over the past 150 years showed an erosion rate of 22-32 cm/yr, whereas calculations over the past 7k years (of inferred history) indicated 2-6 cm/yr (Hurst M D et al, 2016). Unfortunately these results were interpreted as an acceleration in erosion in recent times rather than due to the different methodologies they used. But they were comparing different quantities, like apples with oranges! So coastal cliffs comprised of soft rock like limestone can erode at rapid rates.
Appendix B: Different explanations of geological history
The earth’s geological and climatological history has determined the current geomorphological and geological structure of the earth. At present there are two main explanations of the earth’s geological and climatological history. One (Biblical) is based on recorded history in the Bible and the other (Uniformitarian) is based on assuming that the present (processes today) is the key to the past (ancient processes) and on the hypothetical geologic time scale. The biblical explanation allows for catastrophic events (such as the flood of Noah), whereas the Uniformitarian explanation minimizes the role of catastrophic events (because it has a preference for gradual events). The biblical explanation mainly involves rapid processes over short periods of time, whereas the Uniformitarian explanation mainly involves slow processes over long periods of time.
Biblical explanation – The global flood about 4.5k years ago and associated tectonic activity and volcanism produced enormously thick sequences of sedimentary rocks over a short period of time. Fossils represent the order of burial during the flood. The flood was followed by an ice age during which there were volcanic and glacial impacts.
Uniformitarian explanation – Sea levels changed gradually over millions of years to produce the enormously thick sequences of sedimentary rocks that record the long history of geological time. Fossils represent the evolution of species. There were multiple ice ages over millions of years. The most recent ice age ended about 10k years ago.
Some dates associated with these two explanations are shown in Table 2. Their timescales deviate further apart from each other as one goes backward in time. Over a time period of 4.5k years the age calibration factor (between the two explanations) decreases from 1.0 to 0.0017. And by the beginning of the flood the age calibration factor is 0.0000056. So the two time scales deviate greatly during the flood. As the uniformitarian dates are said to be supported by radiometric dating, this shows that the assumptions used in radiometric dating are invalid during the flood. Although radiometric dating may be useful for relative dating in this time period, it’s erroneous for absolute dating. This indicates that indirect measurement methods (like radiometric dating) can be unreliable when they are not calibrated against real measurements (like historical records).
Table 2. Comparison between historical dates according to the Biblical and uniformitarian time scales.
|Event||Biblical age (yrs BP)||Uniformitarian age (yrs BP)||Age calibration factor (Ba/Ua)|
|Sea level restored to current levels||3.8k||7k||0.54|
|Beginning flood||4.501k||800m||5.6 x 10-6|
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Laker C H, 2016, “Shore platform classification of central-southern NSW in relation to morphological variability and risk of drowning”, University of Wollongong.
Premaillon M, Regard V, Dewez J B, Auda Y, 2018, “GlobR2C2 (Global Recession Rates of Coastal Cliffs): a global relational database to investigate coastal rocky cliff erosion rate variations”, Earth Surf. Dynam., 6, 651–668, 2018.
Rosser N J, Brain M J, Petley D N, Lim M, Norman E C, 2013, ‘Coastline retreat via progressive failure of rocky coastal cliffs’, Geology, 41(8), p. 939-942.
Walker T, 2015, “A preliminary age calibration for the post-glacial-maximum period”, J Creation, 29, 1, 6-8.
Written, October 2019