Why Would Such KwaZulu-Natal Homes Get Washed Away During Flooding? : 無料・フリー素材/写真
Why Would Such KwaZulu-Natal Homes Get Washed Away During Flooding? / Axel Bührmann
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Built on sloping, antique sand dunes prone to massive mudslides. Just look at these. As Professor Anthony Turton explains: To be exact, professor Turton adds: "the simple reality is that between the Umzimkulu in the south and the Umlazi in North, there is a precisely defined geological province. The main feature is a basement consisting of igneous rock originating in volcanic and tectonic events over geological timescales measured in billions of years. That same region is bounded in both the north and south by a tectonic feature associated with rifting and faulting. Oribi Gorge is a feature of those tectonic forces.Onto that basement we find an unconsolidated overlay of sand and clay. This is rich in iron oxide and is a reddish colour as a result. The overlay is the result of geomorphology measured in a shorter timescale of millions of years, as opposed to the basement feature that is the result of a much older timescale measured in billions of years.This younger formation is the result of two sculpting forces - wind and water. The area used to be coastal wetland, and as sea levels rose and fell with successive warmer and cooler paleo climates, we find a layering of aeolian formations deposited above hydraulically deposited formations. The aeolian formation is characterised by wind driven dunes that mobilized particles of sand and clay of different fractions. Those sand dunes were characterised by rolling wavelike formations, all along the coastal area. These were consolidated over time by forest and grassland vegetation, which stabilised them.This is evident where there is no surface striking rock formation and can be seen in the valleys scoured by rivers. Those valleys reveal the underlying geological formation of rock, now manifesting as meanders with relatively steep sides carved out by the action of water in paleo flood events. This means that flooding is what has shaped the region and is an entirely natural ocurrance with a history covering geological timescales.This is further evidenced by the sedimentary deposition of silt in the ocean, for a considerable distance offshore. We see that process playing out right now as muddy seawater all along the coast, stretching almost to the horizon. That muddy water consists of the fine clay fraction of the eroded soil profile, held in suspension as a colloid and therefore persistent over time, but always associated with a flood event.This is a simplistic description of a complex reality, but it shows that the geomorphology has been driven mostly by hydraulic and aeolian forces, at least insofar as the consolidated sand dunes are concerned. Tectonic events drove earlier geomorphology, manifest as rifting and faulting, but the more recent drivers have been floods.Therefore flooding is a characteristic of the geological province, so policy designed to mitigate risk ought to be based on the assumption that future flood events will be a reasonably predictable driver of risk. Stated differently, and in simple form, the following is true of the coastal region between the Umzimkulu and Ulmazi rivers.1) The absence of surface striking basement geology along the coastal strip renders the region geotechnically unstable and in need of precise building standards that must be strictly enforced.2) Flooding is a natural occurrence that has shaped the geomorphology of both the land and immediate offshore sub-sea terrain.3) Climate variability is a natural process, exacerbated by anthropogenic intervention, and is likely to feature an increase in extreme events, at least in our lifetime.These three factors ought to be built into policy if the human population, and financial investment in the region, is to be protected in future.Note that this is a gross simplification of a complex reality, rendered in such a way as to make it understandable to policymakers in government, insurance company decision makers, and investors deciding to purchase real estate."As Professor Anthony Turton explains: "the simple reality is that between the Umzimkulu in the south and the Umlazi in North, there is a precisely defined geological province. The main feature is a basement consisting of igneous rock originating in volcanic and tectonic events over geological timescales measured in billions of years. That same region is bounded in both the north and south by a tectonic feature associated with rifting and faulting. Oribi Gorge is a feature of those tectonic forces.Onto that basement we find an unconsolidated overlay of sand and clay. This is rich in iron oxide and is a reddish colour as a result. The overlay is the result of geomorphology measured in a shorter timescale of millions of years, as opposed to the basement feature that is the result of a much older timescale measured in billions of years.This younger formation is the result of two sculpting forces - wind and water. The area used to be coastal wetland, and as sea levels rose and fell with successive warmer and cooler paleo climates, we find a layering of aeolian formations deposited above hydraulically deposited formations. The aeolian formation is characterised by wind driven dunes that mobilized particles of sand and clay of different fractions. Those sand dunes were characterised by rolling wavelike formations, all along the coastal area. These were consolidated over time by forest and grassland vegetation, which stabilised them.This is evident where there is no surface striking rock formation and can be seen in the valleys scoured by rivers. Those valleys reveal the underlying geological formation of rock, now manifesting as meanders with relatively steep sides carved out by the action of water in paleo flood events. This means that flooding is what has shaped the region and is an entirely natural ocurrance with a history covering geological timescales.This is further evidenced by the sedimentary deposition of silt in the ocean, for a considerable distance offshore. We see that process playing out right now as muddy seawater all along the coast, stretching almost to the horizon. That muddy water consists of the fine clay fraction of the eroded soil profile, held in suspension as a colloid and therefore persistent over time, but always associated with a flood event.This is a simplistic description of a complex reality, but it shows that the geomorphology has been driven mostly by hydraulic and aeolian forces, at least insofar as the consolidated sand dunes are concerned. Tectonic events drove earlier geomorphology, manifest as rifting and faulting, but the more recent drivers have been floods.Therefore flooding is a characteristic of the geological province, so policy designed to mitigate risk ought to be based on the assumption that future flood events will be a reasonably predictable driver of risk. Stated differently, and in simple form, the following is true of the coastal region between the Umzimkulu and Ulmazi rivers.1) The absence of surface striking basement geology along the coastal strip renders the region geotechnically unstable and in need of precise building standards that must be strictly enforced.2) Flooding is a natural occurrence that has shaped the geomorphology of both the land and immediate offshore sub-sea terrain.3) Climate variability is a natural process, exacerbated by anthropogenic intervention, and is likely to feature an increase in extreme events, at least in our lifetime.These three factors ought to be built into policy if the human population, and financial investment in the region, is to be protected in future.Note that this is a gross simplification of a complex reality, rendered in such a way as to make it understandable to policymakers in government, insurance company decision makers, and investors deciding to purchase real estate." |
| 撮影日 | 2022-03-14 12:39:50 |
| 撮影者 | Axel Bührmann , Here, South Africa |
| タグ | |
| 撮影地 | Umdoni, KwaZulu-Natal, South Africa 地図 |