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Art by Sylvain sarrailh

What kind of event would we need to have 1km deep fissures spanning out across the planet.

I can work with a hypothetical scenario where the planet might have had some sort of tectonic issue causing these fissures to open up all over the place, but what kind of event would that look like?

Can be a man made event or natural.

Gap at the top 50 meters or greater.

1Km Deep at least.

Must be a Habitable planet similar to earth

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    $\begingroup$ how wide do they need to be , deep narrow fissures are not impossible. $\endgroup$ – John Dec 21 '19 at 5:09
  • $\begingroup$ 50 meters or more I could work with. $\endgroup$ – Sandorien Dec 21 '19 at 6:35
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    $\begingroup$ Yeah that's not going to happen, that would require the tectonic plate to move 50 meters in 100 years, which is orders of magnitude too fast. $\endgroup$ – John Dec 21 '19 at 16:10
  • $\begingroup$ I have updated the post to see if we can come up with any ideas around that. $\endgroup$ – Sandorien Dec 22 '19 at 7:12
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    $\begingroup$ Does your planet have to be habitable by humans? If not just look at Europa: It’s ice-crust is heavily cracked. $\endgroup$ – Tonny Dec 22 '19 at 9:52
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Look at the Gran Canyon, it has been made by a combination of factors: river flow and tectonic uplift.

The Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (6,093 feet or 1,857 meters) [...]

The Grand Canyon is part of the Colorado River basin which has developed over the past 70 million years,[15] in part based on apatite (U-Th)/He thermochronometry showing that Grand Canyon reached a depth near to the modern depth by 20 Ma. [...]

The great depth of the Grand Canyon and especially the height of its strata (most of which formed below sea level) can be attributed to 5–10 thousand feet (1,500 to 3,000 m) of uplift of the Colorado Plateau, starting about 65 million years ago (during the Laramide Orogeny). This uplift has steepened the stream gradient of the Colorado River and its tributaries, which in turn has increased their speed and thus their ability to cut through rock (see the elevation summary of the Colorado River for present conditions).

It's extremely unlikely that you can get a similar thing in 100 years.

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You just can't get anything that lage quickly, you can have small fissures form quickly (look at iceland) but anything near the scale you want will take millions of years to form and is not a fissure as much as it is a canyon of valley. On a world without plate tectonics it is possible but not earth.

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