<p>From a technical point, landslides occur when the stability of the ground is exposed to forces and conditions that cause failure of the slope material. From this point of view we need to consider the material of a specific slope but also any conditions that can cause failure. A very common cause for failure is increased moisture or even water pressure in the slope material. Hence intense rainfall is a prime condition to initiate slope failure. Depending on the climate regions considered, snow and ice melt contributing water can also be a factor. Melt is basically governed by temperature. In mountainous regions melting of permafrost may yield increased risks for slope failure.</p>
<p>The presence of water in soil is thus a prime factor for landslides so depending on where the slopes are located, one need to consider both melting of frozen ground and precipitation. Given the global warming cold regions will suffer from permafrost melting causing slopes to become unstable but slopes may also experience an increase in precipitation, particularly increased intensity of precipitation that can cause slope failure. In the case of cold regions problems will be primarily a function of temperature coupled to snow and ground frost melting, a typical spring phenomena. In other regions the risks are coupled to precipitation which is coupled to the frequency and magnitude of rain fall events. The frequency of land slides will thus be strongly coupled to reaching conditions causing the slope stability to be reduced.</p>

CC BY-SA 4.0
2024-09-06T17:17:06.910Z
2024-09-06T17:17:06.910Z
Peter Jansson
<p>In addition to Peter's quite good, if very general, answer you also need to consider the underlying material in the slope. Many slope failures in New Zealand are caused by the lubrication effect of water on a potential failure plane, often in the form of mudstone or other clay strata. As to the odds those are very weather dependent but even in <a href="https://hwe.niwa.co.nz/event/February_2004_North_Island_Storm" rel="nofollow noreferrer">extreme weather events</a> it is vanishingly rare to see more than 10% of the slopes in any given <a href="https://en.wikipedia.org/wiki/Drainage_basin" rel="nofollow noreferrer">drainage basin</a> fail, even less in forested regions where tree roots hold the slopes together to greater depths. Large slope failures are rarer than small ones. Human infrastructure plays a role as well, especially road cuttings, many human infrastructure projects result in breaks to the natural slope of the land this results in instabilities that <em>will</em> settle to the natural <a href="https://en.wikipedia.org/wiki/Angle_of_repose" rel="nofollow noreferrer">angle of repose</a> of the material of the slope. The three events you note all occurred during heavy rain events and the collapses all happened along roads. All three areas indicated are also subject to regular seismic activity which can destabilise slopes that are otherwise at repose because it creates an effective increase in <a href="https://en.wikipedia.org/wiki/Pore_water_pressure" rel="nofollow noreferrer">pore pressure</a> due to vibration.</p>

CC BY-SA 4.0
2024-09-08T12:33:34.140Z
I think i understand. So the frequency of landslides in certain reas is dependant on various conditions like the weather and stability of slopes.  I also read that Asia is especially vulnerable to landslides, most happen there. My question is do landslides happen often enough that multiple landslides happening across the planet on the same day is a probable occurance. I asked the question elsewhere and was told landslides happen every day.
Uno
CC BY-SA 4.0
2024-09-09T02:20:22.493Z
@Uno They do happen every day, but that's not an especially useful answer. Asia has a lot of landslides at certain times of year, this is primarily due to two colliding factors, 1. Asia has a lot of young mountains with slopes that haven't eroded to a stable angle (largely due to the ongoing mountain building of the Himalayas). 2. Asia has the monsoon, the continent is relatively dry for months then sodden which means that the ground goes from damp but stable to liquid, sometimes in mere hours.
Ash
CC BY-SA 4.0
2024-09-09T08:25:56.720Z
I do appreciate you going into a little bit of detail on the nature of landslides. I guess i was unaware and surprised about how common they are. Given i grew up in the rural mountains of South Africa and have never heard of them happening a lot in my area. It makes sense why now. Thank you for taking the time to explain.
Uno
CC BY-SA 4.0
2024-09-07T07:51:16.590Z
2024-09-07T07:51:16.590Z
Ash
<p>Recently, i noticed that on the 27th of August, 3 landslides occured across 3 different countries : Italy,Japan and Yemen.</p>
<p><a href="https://www.unocha.org/publications/report/yemen/yemen-flash-flood-update-no-03-milhan-district-mahwit-governorate-29-august-2024-enar#:%7E:text=Heavy%20rainfall%20on%20the%20evening,causing%20landslides%20and%20falling%20boulders" rel="nofollow noreferrer">https://www.unocha.org/publications/report/yemen/yemen-flash-flood-update-no-03-milhan-district-mahwit-governorate-29-august-2024-enar#:~:text=Heavy%20rainfall%20on%20the%20evening,causing%20landslides%20and%20falling%20boulders</a>.</p>
<p><a href="https://japantoday.com/category/national/three-missing-as-%27extremely-strong%27-typhoon-nears-japan" rel="nofollow noreferrer">https://japantoday.com/category/national/three-missing-as-'extremely-strong'-typhoon-nears-japan</a></p>
<p><a href="https://www.reuters.com/world/europe/landslide-southern-italy-leaves-woman-son-missing-feared-dead-2024-08-28/#:%7E:text=ROME%2C%20Aug%2028%20(Reuters),and%20feared%20to%20have%20died" rel="nofollow noreferrer">https://www.reuters.com/world/europe/landslide-southern-italy-leaves-woman-son-missing-feared-dead-2024-08-28/#:~:text=ROME%2C%20Aug%2028%20(Reuters),and%20feared%20to%20have%20died</a>.</p>
<p>I understand that they a pretty common, but how statistically probable are landslides to occur in 3 different countries across the planet on the same day?</p>
<p>Edit:I'm not completely in the know about landslides but i would say landslides that are big enough to cause problems for a community like the ones in the news articles i linked. I know that even small lanslides pose a threat. The landslides don't necessarily have to happen in a populated place though.</p>

CC BY-SA 4.0
2024-09-06T11:25:54.397Z
I hope the edit was enough clarification. I don't have in-depth knowledge about the field.
Uno
<time><natural-disasters><land-surface><natural-conditions><land>
How often do landslides occur?
Uno
# How often do landslides occur?

(Asked by: username_0 on 2024-09-06)

Recently, i noticed that on the 27th of August, 3 landslides occured across 3 different countries : Italy,Japan and Yemen.

[https://www.unocha.org/publications/report/yemen/yemen-flash-flood-update-no-03-milhan-district-mahwit-governorate-29-august-2024-enar#:~:text=Heavy%20rainfall%20on%20the%20evening,causing%20landslides%20and%20falling%20boulders](https://www.unocha.org/publications/report/yemen/yemen-flash-flood-update-no-03-milhan-district-mahwit-governorate-29-august-2024-enar#:%7E:text=Heavy%20rainfall%20on%20the%20evening,causing%20landslides%20and%20falling%20boulders).

[https://japantoday.com/category/national/three-missing-as-'extremely-strong'-typhoon-nears-japan](https://japantoday.com/category/national/three-missing-as-%27extremely-strong%27-typhoon-nears-japan)

[https://www.reuters.com/world/europe/landslide-southern-italy-leaves-woman-son-missing-feared-dead-2024-08-28/#:~:text=ROME%2C%20Aug%2028%20(Reuters),and%20feared%20to%20have%20died](https://www.reuters.com/world/europe/landslide-southern-italy-leaves-woman-son-missing-feared-dead-2024-08-28/#:%7E:text=ROME%2C%20Aug%2028%20(Reuters),and%20feared%20to%20have%20died).

I understand that they a pretty common, but how statistically probable are landslides to occur in 3 different countries across the planet on the same day?

Edit:I'm not completely in the know about landslides but i would say landslides that are big enough to cause problems for a community like the ones in the news articles i linked. I know that even small lanslides pose a threat. The landslides don't necessarily have to happen in a populated place though.

**Tags:** time, natural-disasters, land-surface, natural-conditions, land

> **Comments:**
> **username_0**: I hope the edit was enough clarification. I don't have in-depth knowledge about the field.  

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## 2 answers

### Answer by username_1 on 2024-09-06. Score: 1

From a technical point, landslides occur when the stability of the ground is exposed to forces and conditions that cause failure of the slope material. From this point of view we need to consider the material of a specific slope but also any conditions that can cause failure. A very common cause for failure is increased moisture or even water pressure in the slope material. Hence intense rainfall is a prime condition to initiate slope failure. Depending on the climate regions considered, snow and ice melt contributing water can also be a factor. Melt is basically governed by temperature. In mountainous regions melting of permafrost may yield increased risks for slope failure.

The presence of water in soil is thus a prime factor for landslides so depending on where the slopes are located, one need to consider both melting of frozen ground and precipitation. Given the global warming cold regions will suffer from permafrost melting causing slopes to become unstable but slopes may also experience an increase in precipitation, particularly increased intensity of precipitation that can cause slope failure. In the case of cold regions problems will be primarily a function of temperature coupled to snow and ground frost melting, a typical spring phenomena. In other regions the risks are coupled to precipitation which is coupled to the frequency and magnitude of rain fall events. The frequency of land slides will thus be strongly coupled to reaching conditions causing the slope stability to be reduced.


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### Answer by username_2 on 2024-09-07. Score: 0

In addition to username_1's quite good, if very general, answer you also need to consider the underlying material in the slope. Many slope failures in New Zealand are caused by the lubrication effect of water on a potential failure plane, often in the form of mudstone or other clay strata. As to the odds those are very weather dependent but even in [extreme weather events](https://hwe.niwa.co.nz/event/February_2004_North_Island_Storm) it is vanishingly rare to see more than 10% of the slopes in any given [drainage basin](https://en.wikipedia.org/wiki/Drainage_basin) fail, even less in forested regions where tree roots hold the slopes together to greater depths. Large slope failures are rarer than small ones. Human infrastructure plays a role as well, especially road cuttings, many human infrastructure projects result in breaks to the natural slope of the land this results in instabilities that *will* settle to the natural [angle of repose](https://en.wikipedia.org/wiki/Angle_of_repose) of the material of the slope. The three events you note all occurred during heavy rain events and the collapses all happened along roads. All three areas indicated are also subject to regular seismic activity which can destabilise slopes that are otherwise at repose because it creates an effective increase in [pore pressure](https://en.wikipedia.org/wiki/Pore_water_pressure) due to vibration.

> **Comments:**
> **username_0**: I think i understand. So the frequency of landslides in certain reas is dependant on various conditions like the weather and stability of slopes.  I also read that Asia is especially vulnerable to landslides, most happen there. My question is do landslides happen often enough that multiple landslides happening across the planet on the same day is a probable occurance. I asked the question elsewhere and was told landslides happen every day.  
> **username_2**: @username_0 They do happen every day, but that's not an especially useful answer. Asia has a lot of landslides at certain times of year, this is primarily due to two colliding factors, 1. Asia has a lot of young mountains with slopes that haven't eroded to a stable angle (largely due to the ongoing mountain building of the Himalayas). 2. Asia has the monsoon, the continent is relatively dry for months then sodden which means that the ground goes from damp but stable to liquid, sometimes in mere hours.  
> **username_0**: I do appreciate you going into a little bit of detail on the nature of landslides. I guess i was unaware and surprised about how common they are. Given i grew up in the rural mountains of South Africa and have never heard of them happening a lot in my area. It makes sense why now. Thank you for taking the time to explain.  

---

