IMPORTANT: THIS IS A TERRAFORMING METHOD INSPIRED BY THE NOAH FLOOD AND NOT AN ARTICLE ABOUT THE BIBLICAL FLOOD!
In Terraforming, a Noah Flood is a violent process in which a massive amount of liquid water starts flowing on a planet or moon. The water might have existed on the planet or it is brought from somewhere else. The result is formation of oceans and a major change in Geography, caused by erosion and sedimentation.
The flood is suspected to occur on the vast majority of rocky planets during terraforming events.
Reason in terraforming Edit
The main reason for creating a giant artificial flood is to create oceans, which is vital in order to make a planet habitable. In addition, this is the best way to ameliorate the Geography of a planet where no liquids have been flowing.
Source of water Edit
In order to create oceans where they have not been, we need to use existing water or to bring water from other sources.
Melting ices. Some planets, like Mars, are supposed to have ice trapped beneath their surface. In this case, once we add Greenhouse Gases, the ice will start to melt and water will flow. The speed with which water melts varies, but on a planet like Mars, if there is enough water, we can see a massive flood.
Atmospheric water. Other planets, like Venus, have all their water in gaseous phase, inside the atmosphere. However, many scientists suggest that water cannot be kept for too long in the atmosphere, because ionizing radiations will break it into hydrogen and oxygen. While oxygen can remain in the atmosphere, hydrogen will be lost fast into outer space.
Artificial atmospheric water. One good way to bring water to a planet is by diverting comets. However, if the planet has a dense atmosphere, like Venus, majority of comets will disintegrate before reaching ground and will make no craters. Water will remain in the atmosphere until we cool the planet enough for rains to occur. And even if the planet lacks a dense atmosphere, an intense comet bombardment can send it to a runaway greenhouse effect, in which most of the water will be in the atmosphere.
Artificial surface water. Some celestial bodies need water for terraforming, but cannot host a large atmosphere. A good example is Luna, or our Moon. In this case, comets will be slowed down as much as possible, sent to a low orbit and then allowed to impact the planet. For the Moon, since its gravity is about 6 times smaller then Earth's, the impact force of a de-orbiting comet will be about 36 times smaller then on Earth. This could allow us to send comets to the Moon without creating major impact craters.
Flood impact Edit
A lot of research have been done by people who studied if Noah's flood was real or not. Their work is very useful for us, because their models can be applied to other planets and moons.
According to the text, it rained for 40 Earth days, until sea level raised above the highest mountains. Then, water receded probably to the former level. However, during terraforming processes, it will not be quite like this. Water will be inserted on a longer period of time, it will not rise above the highest mountains and it will not retreat.
Erosion and sedimentation Edit
The flood will cause two processes: erosion and sedimentation.
Erosion. Everyone can imagine what would happen if you send a huge river, like the Nile, in the valley of a small stream. It will erode its valley very fast, creating huge canyons. The process will be extremely violent where rapids occur, but it will not affect too much mountain ranges. Mountain tops will remain at the same height. However, if water accumulates behind a mountain range (for example a crater rim), at some point it will rise above the mountains, forming a huge waterfall that will erode fast all obstacles, resulting in a huge secondary flood downstream, while the upstream lake will decrease in size fast.
If we think about a large river basin, like the Danube or the Mississippi, there will be a huge amount of water flowing, like a river over 300 km wide. With such a force, that river will blast away all obstacles, including solitary mountains and large rocks.
In the beginning, erosion will also occur on the bottom of future oceans. So, when the oceans will increase in size, water will enter on new created river valleys, forming estuaries.
Sedimentation. Downstream from rapids, sediments will accumulate, creating large plateaus. Also, if there are depressions (like flooded craters), they can be silted with sediments brought from upstream. The process will result in the formation of large inland deltas.
A significant part of the sediments will be carried to the oceans. However, since oceans will grow in size, sediments will be covered with water and will not form deltas.
Combined erosion and sedimentation. An interesting phenomena will happen in some depressions. Suppose water accumulates behind a barrier, that works like a natural dam. Behind the dam, sediments are brought from upstream and try to silt-up the lake. As water flows over the dam, it starts to erode. The more erosion occurs, the more water flows from the dam. In the end, most of the dam is eroded and most of the lake is drained. Upstream, rivers start to erode the silt they have deposited, creating valleys and filling the remaining lake.
Streams can erode places with a higher slope, depositing sediments where the slope is lower. however, at some point, when the amount of sediments from upstream decreases, downstream, erosion can occur. In this case, sedimentation occurs further away.
Categories of floods Edit
Ice melting floods. They are created when we increase temperature and force ices to melt. In this scenario, it all depends, based on where the water is located. If water is located downstream, it will only melt and create oceans, without a significant flood, except for the coastline.
It is possible that the water is not uniformly distributed (for example, it is located at the poles, in large ice caps). In this scenario, areas without ice will remain almost unchanged, while other areas will be strongly affected by erosion and sedimentation.
Regions covered with ice will undergo an interesting transformation. At first, the ice layer will protect the ground from erosion. In this phase, there will be rivers flowing above ice, creating deeper and deeper canyons, until they reach the ground. Then, erosion will start, mainly along the rivers. Land between rivers will be less affected, because, when finally they will finally be exposed, there will be not much water to erode them. Also, rivers might carry sediments and deposit them on top of an ice layer. The ice will finally melt, but a significant part of the sediments will remain on ground.
Another interesting phenomena will occur where there is a mixture of rock and ice. As ice will melt, the rock will be left behind, maybe under the form of mud, of sand or of rocks with high porosity. Complex networks of caves might be left behind.
For ice to melt, it is required a significant amount of heat. Also, planets with ice are usually away from the comfort zone, so they don't receive enough heat from their parent star. The whole process will take many decades. Rivers will not be too large nor very violent, but since the process will be long enough, well established hydrologic networks will be created.
An estimated model of an ice-melting flood for terraforming Mars is the equivalent of a daily rain of 82 liters per square meter for 10 Earth years. This is like an average rain, but that runs continuous. It would require 1000 square meters to generate a river with a flow of 1 liter per second and 1 square km to produce a river of 1 cubic meter per second.
Atmosphere condensing floods. They are produced when water condenses from the atmosphere, as the planet cools down. They can be very violent. As more water condenses, the greenhouse effect decreases and the planets cools, forcing even more water to rain. It is not known for how long this process can take, but certainly not for many years.
Atmosphere condensing floods are global and send an almost equal amount of water to all regions of the planet. This is an advantage, as the process can ameliorate majority of Geographic features in the same time.
Because atmosphere condensing floods occur very fast, they have the strongest effect on Geographic features. They are the closest thing to Noah's flood.
An estimated model of atmosphere condensing flood, for Venus, is of 822 liters per square meter for an Earth year. This equals with 0.5 liters per minute. It will require 100 square meters to produce a river with a flow of 1 liter per second and 0.1 square km to produce a river with a flow of 1 cubic meter per second.
Given the huge amount of water that will flow, many places of the planet will be completely transformed beyond recognition.
Liquid water floods. They are created in case of planets and moons with low gravity, unable to sustain a dense atmosphere. In this case, comets are made to land as soft as possible. Comets drop on the surface, creating smaller craters. During the process, they melt-up or vaporize, but the water is condensed in a limited area. The process is repeated as many times as needed.
Impact regions are chosen for each comet diversion. The target or many impacts is a barrier in front of a future river.
These kind of floods are not massive. If the number of impacts is too high, temperature can rise too much and we can lose much of the atmosphere. It is good to notice that planets and moons where this technique is required are celestial bodies with little gravity, where water erosion is less powerful. So, the effect on Geographic features is less visible.
Secondary floods. Sometimes, scientists would want to do a second flood to a planet. This might be require if the Geographic features are not as desired, to create new and larger river valleys faster.
There is also another scenario, when secondary floods occur. For example, if a natural dam holding a lake is eroded fast. Like the collapsing of a dam, this can result in a massive flood downstream.
After the flood Edit
The flood will alter many Geographic features on the planet. It will create large valleys, but still the result will not be like a new Earth.
First of all, as the rivers will retreat, they will consist of a network of lakes and rapids. This is just what you would see on any river on Earth, if you remove almost all of its water. There will be many small lakes and dunes along the former riverbed. It will take time, but not too long, for a new equilibrium to occur and for new riverbeds to form on the former ones. The former riverbeds will in fact become valleys.
A second change will be in sedimentation areas. There, land was fluffy and will start to condense. So, places very close to a lake can become submerged in time. In the same way, in a sedimentary plain, small depressions might form. They will be filled with water.
Many rivers that erode their valleys fast, create deep canyons with vertical walls. However, they don't remain in this state for long. The walls can collapse or are further eroded. If a wall collapses, it can create a natural dam.
Another major change is that a flood washes the ground and takes excess salts away. It also can wash soft materials, exposing compact rocks. On the other hand, a massive flood is strong enough to smash rocks and create soft ground.
A massive flood is required and maybe inevitable during terraforming processes of rocky planets like Venus and Mars. It could be the only way to give a more Earthly shape to crater-themed Geography, which we see on Moon and Mercury.