A Pressing Problem

The Storegga slide is a very interesting event and it merits closer examination as it may be relevant to our situation. The prehistoric event has been thoroughly investigated and studied. This is because the tsunami was such a major disaster and Norway and nearby countries obviously want to know if something like this can happen again. But one particular reason is that gas deposits are believed to have played a role in the landslides. The Norwegian Sea, where the slide occurred, has underwater deposits of natural gas which humans want to pump out so they can use it. As Norway has started to exploit a gas field called Ormen Lange, it has to know if such activities are going to cause a disaster like with Storegga.
About 8,000 years ago, when Britain was connected to Europe by a land bridge and everybody in the region was still in the Stone Age, a massive freak event occurred in the depths of the sea just east of Scandinavia. Three massive landslides, arranged in a line pointing towards Norway, occurred simultaneously. The area that slid was the size of Scotland and it displaced 840 cubic miles of debris, an amount that could cover all of Iceland to a depth of 112 feet. It caused a massive tsunami which produced waves several feet high on Scotland’s shores and waves 20 meters high in Norway. It washed away the land bridge between Britain and Europe. What is remarkable about the landslides is that they slid along a very flat surface that sloped only one or two degrees, the same sloping that a football field has to get rain to run off quickly. So, something big must have caused the huge amount of seafloor to just move around.
One reassuring theory is that the Storegga landslide occurred due to the end of the last ice age and that a similar event will not happen until after the next ice age has ended. What is happening is that Scandinavia is rising from the ocean. That is because during the last ice age, heavy glaciers covered it, pressing it down. When the ice age ended, the glaciers melted away, taking a lot of weight off, so Scandinavia is slowly moving back up. It is like if you press down on your mattress and then release your hand. The area pressed down will slowly rise back up. This movement would have been greater 8,000 years ago and so would have caused great earthquakes. The ice age deposited sediment in the ocean and this sediment would have all failed and slid away due to the earthquakes. So, Norway no longer has dangerous sediment. It provides a good example of the rapid build up of earth which results in landslide as explained later on in the book. So, the ice age produced a great amount of unstable sediment, and it all slid away and is a threat no more. What a relief! It also provides an example of the principle outlined in the same chapter that landslides cannot be much of a threat because unstable land would slide away.
But this is not the end of the matter. Deposits of gas such as natural gas, methane, and hydrocarbons often form under the seafloor, always pressuring to rise to the surface and when they do, often due to an earthquake, the seafloor can be pushed out of the way. That may have been what happened in Storegga but not due to the natural gas. Instead, clathrate hydrate, which is gas compressed into a crystalline form (which can form in pipelines), decomposed and gave off methane. It is possible large amounts of methane escaped, causing a slump in the seafloor that made it slide. This is of worrying concern for the modern world as we want to pump natural gas out from beneath the head-scarp of Storegga, as the subsequent increasing vacancy could create instability. In the future, the United Kingdom will get 40 percent of its gas from right out of where the huge landslides occurred 8,000 years ago. In addition to tsunami risks, the slightest landslide could destroy drilling and rigging infrastructure. It could create a spill of natural gas.
Now, could just principles apply to Pakistan? Obviously, the Arabian Sea has not been affected by the ice age, although maybe the Indus River water input was different back then. There are submarine gas deposits next to Pakistan, particularly in the Makran Trench. The accumulation of sediment has meant our seafloor offshore is soft, porous, and unstable, as well as filled with gases from causes such as decomposing nutrients. There are extensive deposits of methane hydrates from which natural gas can be derived, as Japan recently demonstrated. As Japan continues its work, it is believed this frozen methane could be a potential source of energy to rival oil. Speaking of which, there are abundant deposits of this also in the Arabian Sea.
I believe that this whole thing is a fascinating and complex subject which we really need to study for reasons such as disaster risk. It is the dynamics of the sedimentation of the ocean floor, especially with regards to materials deposited by rivers on land. This is a subject that applies to Pakistan because of the Indus River. There are several questions. Was the flow into the ocean from the Indus Delta different during the last ice age? Did or will human settlement and civilization change the inflow of materials into the Arabian Sea? Will sucking out oil, gas, and methane hydrates cause great changes? What is under the sheet of soft sediment that the Indus has spread all over the seafloor around Pakistan? What effect does this all have on biodiversity and ocean life, since a lot of substances from land are being poured into the sea? The second question is particularly relevant to this one. Farming, which occurs around rivers, induces great changes in the land (from when there was no farming). Changes in the land can decrease or increase the amount of sediment running into the river. Nutrient flow into the river can change enormously. More recently, pesticides and fertilizers can have a big impact on the ocean. We Pakistanis must study such things. They can be useful in so many ways, but one of them is disaster assessment, especially with tsunamis. As a matter of fact, this subject is the reason behind one of the biggest disasters in the history of the planet, 360 million years ago.
It should be kept in mind that the five big mass extinctions of the last 500 million years, the most recent of which killed the dinosaurs, are five big disasters. They are the five biggest natural disasters ever. They were caused by rapid natural changes, which is worrying since humans now are causing very rapid artificial change in all aspects of the planet. But it is particularly relevant considering the second mass extinction, which ended the Devonian period. The period was spent with plants evolving to be on land. Over time, they grew bigger and bigger, but because they still reproduced with spores, which required a certain degree of water dependency, they did not grow far from water bodies and wet areas. In fact, the world was one big rice field! They were at least helped by the fact that the Devonian was a very wet world.
There was a strange thing, though. There is a certain phenomenon whereby water receives a saturation of nutrients which causes an overgrowth of algae. Since algae consume oxygen in large amounts when they die and decompose, this makes the water be without oxygen, anoxic, in other words. Now, anorexic conditions seemed to be very common in the Devonian period. A lot of freshwater was starved of oxygen and was just a stagnant sludge. This resulted in many animals evolving to live in this water by breathing air, such as snails, scorpions, eurypterids, a single placoderm called Brothlyolepsis, lungfish, and returning from the land, insects, which had a gill flap grew to be a paddle, later on evolving into wings. The cause of these conditions was that vegetation was densely crowded around the water and they had an enormous amount of nutrients run off. Things continued this way steadily for several million years but any time, catastrophe always lurked. The anoxia could spread and creatures could die off en masse in previously oxygenated freshwater bodies. The algal blooms could also spread into the ocean and cause suffocating conditions there.
Anoxic events are known to have occurred in Earth’s vast oceans. The oceans basically have an oxygen circulatory system built in. But it can be disrupted or deteriorate at times. Obviously, the entire oceans can never have all their oxygen disappear. But the marine ecosystem is a very fragile one. Its backbone is phytoplankton which float at the surface and feed on nutrients. Nutrients in the oceans are scarce. This is because the ocean is so big that biomass is thinly distributed. Anoxia is sometimes caused by a huge influx of nutrients concentrated in one area, resulting in that area having not nourishing phytoplankton but algal blooms which cause large areas of water to be deprived of oxygen. This causes a major disruption in the oceanic oxygen cycle and large scale extinction events can occur.
At the end of the Devonian period, spore plants evolved into seed plants. These new plants had deeper roots and could colonize drier areas away from water. The process seemed to be relatively rapid for evolution, and at the end of the Devonian, a fully fledged tree called Archaeopteris spread like plague. Along with this came a spread of breaking up of the land into soil. This resulted in an increase in weathering which caused ions, food for algae, to run into the water. Plants spread so much that a massive amount of nutrients ran off into the freshwater and then it ran off into the ocean like what the Indus River does today. So, there were massive algal blooms all over the oceans causing a general depletion of oxygen. The ocean ecosystem was so disrupted that a mass extinction occurred. Its biggest casualties were the dinosaurs of the ocean at the time, fish called placodermi which had armoured heads. They were the dominant animals but they completely died out, a testament to how big the disaster was.
We are not sure this really was the cause of the Devonian end extinction, but there is evidence for this. Among other things, unlike other mass extinctions, the Devonian ending was not very rapid and it is indicated that it took place over a long time, possibly 26 million years. Since evolution is slow, this fits in with the theory that the extinction was caused by plant evolution. The thing is, this much time should have given life time to adapt, but they failed to do so, meaning the disastrous run off of nutrients was really very terrible. Now, this has relevance to what is happening now with the development of civilization, which is happening far more rapidly than any change in the Devonian.
A repeat of what happened at the end of the Devonian is occurring today. For example, farming in Australia is resulting in phosphate nutrients running off into the ocean and causing enormous damage to the Great Barrier Reef. This one fact should be enough to send us into extreme alarm.


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