Some of the most important events in the history of both Earth and Mars, including those of the biosphere, appear to be related to catastrophic periods of considerable hydrological change. Megaflood events have occurred, though at different times on Earth and Mars and have affected both planetary climatic systems, thus it is necessary to study them. Martian climate in the past was closer to Earths than it is today, and it is plausible to say that Earth's climate, in the past, and indeed could be in the future, similar to Mars'. Therefore, it is essential to discuss the similarities and differences between Martian and Terrestrial Megaflood events to help us understand the processes of climate change, geophysics, and the potential for life beyond our own planet. (NASA 2009)
What are Megafloods:
Megaflood events involving sudden discharges of exceptionally large volumes of water are rare; however they can significantly impact landscape evolution, continental-scale drainage patterns and climate change (Gupta 2009). Megaflood events can be define as,
'High energy Megafloods are planetary-scale phenomena associated with glacier outburst settings, glacial lake spillways and the immense outflow channels of mars.' (Baker 2002)
The causes of a Megaflood event vary on Earth and Mars; this is mainly due to the stark contrast in climatic systems (Davie 2002). However, there are some similarities that may influence these Megaflood events that both Earth and Mars experience, such as volcanic and tectonic activity. On both Earth and Mars abrupt and episodic operations of these Megaflood events are major factors in global climatic change and result in spectacular planet-wide climate oscillations.
Earth and Mars are the only two planets to have, or to of had, water circulations and similarities in the weathering processes. (Baker 2009) Both planets have similar landscape features and weathering processes. For example, slopes and mass movements; there are high escarpments on mars and the presence of high winds and fine sediment leads to many similar features on Mars (Summerfield 1991) A notable landform that has caused much speculation amongst geomorphologists has been the formation of channels on Mars, similar to that seen on Earth today. There are three types; the fretted channels, runoff channels and outflow channels. Detailed comparisons between the form of outflow channels and the morphology of the Channelled Scabland of eastern Washington and Oregon in the USA have led to the suggestion that the Martian Channels similarly owe their form to the action of catastrophic floods (Summerfield 1991). Slight variations in the size of these channels and Martian and Terrestrial Megaflood events are due to the differing surface and climatic conditions on both planets. For example, the Megaflood events that formed the Martian outflow channels had maximum discharges comparable to those of Earth's ocean currents and its thermohaline circulation. (Baker 2009)
One of the main factors for this mega-scale environmental change on both earth and mars seem to be associated tectonic and volcanic activity, hence the great quantity of planetary water. Geological record shows that volcano-ice-water interactions are commonly associated with outburst flood channels (Baker et al. 1991). Some Megaflood events on Earth derive from volcano-ice interactions. However the biggest terrestrial floods are associated with glaciers, for example, the Laurentide glacier retreat during the Last Ice Age. On the basis of our current knowledge Mars possesses the largest volcanoes in the Solar System and it is said that for example Olympus Mons which is 24 km high. It is argued by many scientists that these volcanoes are connected to the Martian Megaflood events that occurred tens of millions of years ago, and this could also possibly explain the sheer size of the floods in comparison to Terrestrial Megafloods.
On both Earth and Mars, rapid and sporadic operations of these immense processes have been major factors in global climatic change. On moderately short time scales, by their influence on oceanic circulation, Earth's Pleistocene Megaflood events probably encouraged the Younger Dryas cooling around 12.8 ka ago, and instigated the Bond cycles of ocean-climate oscillation with their related Heinrich events of "iceberg armadas" into the North Atlantic. The Martian Megaflood events are thought to have induced the intermittent formation of a northern plains "ocean," which, coupled with volcanic activity, led to fairly short periods of enhanced hydrological cycling on the land surface. (Barker 2007) This process of episodic short-duration climate change on Mars, operating at intervals of hundreds of millions of years, has parallels in the Neoproterozoic Glaciation of Earth (otherwise known as the "Snowball Earth Hypothesis"). Both phenomena are theorized to involve spectacular planet-wide climate oscillations and associated feedbacks with ocean circulation, land-surface weathering, glaciation, and atmospheric carbon dioxide. It can be sad that the critical factors for mega-scale environmental change on both Mars and Earth seem to be associated tectonics and volcanism, plus the abundance of water for planetary cycling.
The cause of these Megaflood events varies on Earth and Mars. Terrestrial palaeo-flood events are usually associated with glaciations resulting from outbreaks of meltwater in pro or sub-glacial lakes (Burr 2007). The Altai-Mountains in Siberia and the sub-glacial Laurentide ice-sheet floods provide good examples of this association. Whereas the causes of Martian Megaflood events, for example, date back to the Hesperian epoch (3.8-1.8Ga) which originates at 'chaos terrain' for example, areas that released water as pressure increased due to magmatic and/or cryospheric processes (Burr 2007). Martian Megaflood events are also associated with the overflow of impact crater palaeo-lakes and immense upwelling of catastrophic flood flows from subsurface sources (Baker and Milton 1974).
Martian Megaflood events are thought to of happened tens of millions of years ago (around 1 Ga ago) whereas Earths body of water (which takes up around 70% of Earth's surface) has continued throughout the last 3.9 of the planet's history, which has helped to stabilise the planets climate engine. Whereas there's a lack of evidence that the majority of Mars surface was covered by water, it has only had temporary oceans which have not been there throughout the planets history.
There are many similarities and differences between Martian and Terrestrial Megaflood events. In some respects Mars, despite being evidently different, is closer to Earth than any other planet in the solar system. Both planets have, or have had, water circulations and similarities in weathering processes. Channels are also evident on each planet which are thought by scientists to be formed by water. ETC ETC.