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Take our world and look at its surface geography: we have continents and oceans, mountains ridges and canyons, and so on. To my knowledge, most of it has been shaped by tectonic activity (feel free to correct me).

I'm looking into other things that would reshape a world on a large scale. It can be natural phenomena or artificial activities, it can occur over millions of years or in a matter of hours or days, and so on. Anything you can think of, which realistically would be able to change a worlds geography.

To be clear, I'm not looking for "small" regional changes (Mount St. Helen comes to mind), I'm looking for something that would at least reshape a big chunk of a continent, if not more. At the same time, I don't want it to be so extreme to completely destroy the world (eg. Earth's early days meteor shower, which pretty much melted its entire surface, or worse).

Hope it makes sense...

EDIT: I've read some interesting replies so far. I'd like to point out that the changes I'm referring to would be noticeable on a world map. For example, the creation of new landmasses (eg. volcanic islands), their disappearance, or their movement. Seas and oceans, mountain ridges, stuff like that. Is there something that could explain the sea level lowering permanently, leading to new lands emerging? Other than volcanoes (and tectonic activity), are there other ways for mountains to form? Is there something that would explain a huge (as in the sized of a large nation like the US or China) depression to appear? Stuff like that...

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    $\begingroup$ It really matter how you want to reshape a the continent, change the position or entire border of the continent change the things that live on it all haver drastically different answers. , if you means drastically change its continental borders without reliquifling the planet you basically only have tectonic effects and global ice sheets and the latter can only sort of do it. $\endgroup$
    – John
    Feb 13 at 19:08
  • $\begingroup$ Volcanoes. I don't think they are "tectonic activity", although they sometimes are related. $\endgroup$ Feb 13 at 23:55
  • $\begingroup$ I am voting to close without more details beyond "reshape part of a continent" it is unanswerable. the OP could want anything from a change in biomes to splitting the continent in half. $\endgroup$
    – John
    Feb 14 at 2:26
  • $\begingroup$ Sorry for the late reply. To clarify, I was thinking of large changes like the creation (or disappearance) of mountain ranges or seas, or entire continents. While a change of biomes might be considered a big change, that's mostly linked to weather patterns, which is not what I'm looking for. $\endgroup$
    – Mr_Bober
    Feb 14 at 21:18
  • $\begingroup$ Again it depends on what you want to do, erosion can remove a mountain but tectonics is basically the only thing that can build one, sea level can create or remove seas, nothing can remove a continent and leave the rest of the planet intact. you really need to narrow down your question. $\endgroup$
    – John
    Feb 15 at 17:00

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Erosion is a powerful but slow and time consuming process that can make dramatic changes. The best example of this is the Grand Canyon. Carved by a river over at least 17 million years, 5000 to 10,000 feet deep, 277 miles long and 18 miles wide.

Erosion, whether it be due to wind, rain, water flow in rivers, glaciers is a major cause of geology, in the form of mineral grains, boulders and rocks to be mobilized and dispersed over a wide region.

Weathering is another force that reshapes the surface of the Earth. Australia is a perfect example of this. Weathering results in the physical breakdown of the of the surface geology due to weather, thermal stresses, frost, crystal formations and decomposition, oxidation, biological activity, alternating patterns of hydration and dehydration over a very prolonged period of time. The difference between erosion and weathering is erosion causes movement of material, weathering happens in situ.

Fire tolerant plants such as eucalyptus and fire as a result of natural forms of ignition, such as lightening can change the botany of a large region, again see Australia. Eucalyptus has been described as a weedy tree that came to dominate a landscape when less fire tolerant plants became extinct.

Persistent fire or drought over a prolonged period can lead to permanent loss of flora resulting in desertification. Similarly, excessive rain due to climate change can lead to landslides and excessive erosion.

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  • $\begingroup$ all those are pretty small scale on the terms of continents. $\endgroup$
    – John
    Feb 13 at 19:08
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    $\begingroup$ @John but it happens all over the world, all the time. On aggregate, it's huge. $\endgroup$
    – Spencer
    Feb 13 at 23:37
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    $\begingroup$ "Geology is the study of pressure and time. That's all it takes, really. Pressure and time." $\endgroup$
    – Mazura
    Feb 13 at 23:42
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    $\begingroup$ Erosion... And its counterpart, sedimentary deposits. $\endgroup$
    – jcaron
    Feb 15 at 16:07
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    $\begingroup$ @John Deserts can be pretty big. looks at the Sahara, or the Australian Outback $\endgroup$
    – nick012000
    Feb 16 at 12:23
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Asteroid strikes. Anything from a smallish crater to re-liquefying the surface of the planet.

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    $\begingroup$ On that topic, what's the largest crater an asteroid could leave behind, without going into "re-liquefying Earth's crust" scenarios? $\endgroup$
    – Mr_Bober
    Feb 14 at 21:21
  • $\begingroup$ @Mr_Bober not that big on the scale being discussed. the problem is the crust is thin, above a certain size its not a crater anymore it is a massive volcano that changes the tectonics of the planet. $\endgroup$
    – John
    Feb 15 at 16:57
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Glaciers come to mind. Their movements over hundreds or thousands of years can

abrade rock and debris from their substrate to create landforms such as cirques [enclosed valleys from which the glacier scooped up earth], moraines [accumulations of this earth deposited elsewhere], or fjords [narrow inlets surrounded by steep cliffs].

Gone fishing

If you ever fished in the Great Lakes and reeled 8n some perch or walleye, thank the glaciers from the last Ice Age. The Lakes are basically large versions of cirques that became filled with water. From Wikipedia:

The Great Lakes began to form at the end of the Last Glacial Period around 14,000 years ago, as retreating ice sheets exposed the basins they had carved into the land, which then filled with meltwater.[1]

The Great Lakes basin is limited in size because it tends to be walled off by the surrounding moraines from those same glaciers, but the waters in that region flow directly into the Atlantic Ocean without passing through Hudson Bay or the Gulf id Mexico as they otherwise might have done. Thus we have an example of the glaciers affecting a natural process across a continent.

Cited reference

1. Cordell, Linda S.; Lightfoot, Kent; McManamon, Francis; Milner, George (2008). Archaeology in America: An Encyclopedia: An Encyclopedia. ABC-CLIO. p. 1. ISBN 978-0-313-02189-3. Link

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    $\begingroup$ Moraines are fun. 0 to 90+ meters of altitude in 2km (Sopot, Poland) $\endgroup$ Feb 13 at 22:31
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The break of a gateway stopping the sea from enter a lower area, like when a newly breached gateway now called the Strait of Gibraltar filled the Mediterranean Sea with water.

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Another answer that hasn't yet been stated is life. Land plants totally changed weathering patterns. And of course humans have radically altered the world at a global scale, from direct impact (mining, river redirection), to weather patterns from deforestation, to acidification of ocean and sea level rise from climate change.

Edit: Another thing is volcanic activity. Some volcanos aren't associated with tectonics (for example, the hawaiian islands are thought to be caused by hotspots in the mantle). While volcanos can contribute to local changes via eruptions, large enough eruptions can drastically alter the global weather for years at a time, for example via spewing out huge amounts of ash that changes how much sunlight can reach the Earth's surface.

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  • $\begingroup$ I'll have to look more into volcanic activity not linked to tectonics. As for life, humans did partially change the world surface, but on a world map you would barely notice it (except for maybe the Panama Canal). Life does have a large effect on weather and climate, but it's not what I'm looking for. $\endgroup$
    – Mr_Bober
    Feb 14 at 21:26
  • $\begingroup$ @Mr_Bober what you're looking for is totally unclear then. Even simple life can significantly change the landscape of a planet over the course of millions of years. $\endgroup$
    – spacetyper
    Feb 15 at 0:52
  • $\begingroup$ @Mr_Bober what about dams? They create gigantic lakes. I expect you’d notice that before the canal really! $\endgroup$
    – Tim
    Feb 15 at 9:56
  • $\begingroup$ I like this answer, since life has some subtle but very far-reaching effects on climate, erosion, and atmospheric composition, even when completely disregarding human activity. It seems reasonable to think that an earth that was always lifeless would have at least some geographical differences from our current planet. $\endgroup$ Feb 16 at 21:29
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The Netherlands reclaimed land from the sea and built huge dikes to keep back the water.

So human activity consisting of moving dirt also reshapes the world's surface.

Here's a randomly googled youtube video explaining what that consists of: https://www.youtube.com/watch?v=i6DRRHXt-PA

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How about corals? The Great barrier Reef is already quite noticable from space.

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Temperature changes

Lots of possible reasons for that (variation in solar output, variation in the composition of the atmosphere, changes in orbit, rotation or angle of the planet...).

If it goes up, oceans expand (due to melting of ice caps and glaciers and expansion of water), and continents shrink. Inner seas and lakes may on the other hand shrink due to lower precipitations.

It it goes down, the opposite happens.

Also affects weather patterns, which may change forests to deserts. Won't necessarily change the shape of a continent, but will definitely change what it looks like.

Erosion and deposition

Takes matter from one place (erosion) and moves it somewhere else (sedimentary deposits). In extreme cases, this can affect paths of rivers which may switch their output from a sea to an ocean and make that sea shrink or disappear.

Asteroids

See the Moon, the 300 km-wide Vredefort Crater and many others.

Non-tectonic volcanoes

Create islands or mountains, expand land surfaces. Make create tsunamis which may have impacts on land features.

Humans via:

  • Land reclamation. Total area reclaimed currently exceeds $20,000 km^2$.

  • Global warming (see temperature changes).

  • Creation of dams (and thus lakes), rerouting of rivers, irrigation (which may divert output from inner seas/lakes and dry them up)...

  • Deforestation. Affects erosion (see above), irrigation, weather patterns, albedo...

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In the history of our planet there were a handful of volcanic events which shaped parts of continents (specifically, covered them in lava) and are linked to mass extinction events. Nature had an article in 2017.

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Slightly smaller than perhaps what your looking for but does fall under "noticeable on a world map", Nuclear explosions. Specifically there have been plans for "civilian usage" in making ports, canals, tunnels though mountains etc. https://en.wikipedia.org/wiki/Project_Plowshare#Proposals

The plans covered pretty much anything where you need to make a big hole. A new Panama canal though Nicaragua would thus seem to fit the bill for "noticeable".

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Some I don't see mentioned here.

Gravity, esp. the gravity the moon exerts on the ocean, creating tides.

Radiation, esp. solar radiation.

Earth axial tilt, which causes seasons and affects biomes.

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