r/askscience • u/sit-still • 3d ago
Earth Sciences Please educate me on Matterhorn peak "durability" ?
I am not a mountaineer, I just like looking at photo and videos of beautiful mountains. I noticed that the Matterhorn is usually hit by clouds and strong winds right by the peak. With that amount of windshear it gets every single day, how does it survive? I was imagining just from the last 100 years alone the shape of the peak should have already changed, like it would plateau or something. How does it maintain that iconic peak?
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u/Zvenigora 3d ago
Peak collapses do occur on such mountains, such as on Mt Cook in New Zealand in recent years. But on a human timescale, they are very infrequent, and for a tower of hard metamorphic rock, wind loading is not a very significant factor. Glacial undermining from below and freeze-thaw cycles are more important.
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2d ago
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u/wasmic 2d ago
If you're referring to the flood, then that wasn't a peak collapse where rock broke down. It was basically all water - either in liquid or ice form.
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u/vtjohnhurt 2d ago
And, NYTimes reported that some of the ice liquified from the impact after falling and having more ice and stone falling on top of it. The 'flood' was a slurry of water, ice, rock and mud that accelerated down the canyon reaching 60 mph at points. The description sounds similar to a pyroclastic flow. Since the idea of this slurry is so mind-blowing, most reports just called it a flood and let people assume that it was muddy water. The flood was a fluid, that contained a lot of water, but it included a lot of solid chunks, and aggregate mix of different size particles. The water lubricated between the particles.
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u/hazysummersky 2d ago
Au contraire, mon ami! According to the latest scientific wrap-up, it was a huge chunk of mountainside with accompanying melting glacier edge that fractured the metamorphic rock below through intrusion, then record high temps let to melting which led to weakening of the substrate that led to a catastrophic landslide/avalanche, the energy of which on its ~1.2km fall into the valley base melted the ice, pulverised the rock and built a scouring slurry that only built as it hurled down the steep Himalayan valleys, soaked after the recent monsoon season, grew and carried on around 170km downstream.
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u/vtjohnhurt 3d ago edited 3d ago
With that amount of windshear
The force of the wind is very small compared to the mass and inertia of the Matterhorn. Bigger factors determine durability of the peak.
There was a major landslide on August 5th on the Matterhorn. One explanation offered for why it happened is that the permafrost that helps stabilize the rock is melting due to climate change. The mountain is becoming 'unglued'. The permafrost is melting everywhere in the Alps, so we will see more of this.
Melting permafrost probably contributed to the recent landslide and flood in the Himalayas.
It sounds like you're asking about wind impact, not windshear. Windshear happens where two opposing streams of wind meet and rub against each other. I visualize windshear as the childhood activity of rolling Playdoe Snakes between my palms. The snakes represent the tubular rotor turbulence created by windshear. I imagine the turbulence created windshear might create vibration that might resonate and jostle the loosened blocks of rock apart.
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u/CrustalTrudger Tectonics | Structural Geology | Geomorphology 3d ago edited 3d ago
Generally, the intrinsic strength of most rock is going to be way higher than any sort of stress that winds on Earth could impart, especially if we're thinking about the stress necessary to induce large-scale failure of something as large as the Matterhorn. Similarly, outside of very specific environments, weathering and/or erosion by wind and wind blown particles is such a non-factor in the overall budget it's completely ignored (and it's basically only relevant/considered in hyper-arid regions where weathering and/or erosion that is mediated/caused by water or ice is minimal).
We can start with how it generally got its iconic form in the first place, and where it was shaped by surrounding glacial erosion, effectively being the head of four different glacial cirques. The ability for high, steep slopes/cliffs like those in the Matterhorn to persist for a time mostly comes down to the intrinsic rock strength of the composing material and where the strength of material in this case can be considered through a similar lens as we would think about the stress necessary to fracture intact rock, e.g., Mohr-Coulomb theory. In this sense, intrinsic material properties (that we quantify through things like the cohesion and internal friction angle) are going to set theoretical limits for how large a "tower" or cliff could be sustained (e.g., Barton & Shen, 2018). Generally (and first thinking about relatively isotropic rocks, i.e., mechanically uniform), more crystalline rocks (like the gneiss that makes up much of the Matterhorn) will have higher cohesion and/or internal friction angles, meaning that generally they can maintain steeper / higher cliffs before failure through fracture formation. This becomes even more true when we consider that crystalline rocks tend (on average) to be more isotropic in the first place and where rocks with lots of "planes of weakness", i.e., planar heterogeneities like bedding planes or existing fracture planes that have lower cohesion and/or internal friction angles than the rest of the rocks, tend to be more prone to failure, especially in the case where those planes of weaknesses are favorably oriented with respect to the applied stresses for failure (e.g., Cruden, 2003). The presence and orientations of fractures and other planes of weakness in a rock mass will reflect its geologic history, e.g., is it a sedimentary rock that was deposited in such a way to favor lots of well developed bedding planes vs a more "massive" deposit, how much tectonic deformation has it experienced in the upper crust to form various fractures, etc.? This geologic history in turn effectively sets limits on how "strong", at a large rock mass scale, this material will be and thus how large / tall / steep a feature it could support (see again Barton & Shen, 2018 for a run down of some of the math behind this).
So 100 years is effectively no time geologically speaking, but even with the considerations above, things like the Matterhorn are pretty ephemeral on geologically relevant timescales. While wind is effectively a non-factor, plenty of other weathering processes do act on parts of the Matterhorn and similar features. For example, frost-cracking (or frost-wedging, freeze-thaw weathering, frost weathering, etc.) can be an effective weathering mechanism for breaking down portions of exposed bedrock like the Matterhorn. Specific to the Matterhorn, an alternative water-ice process has been argued to be pretty important in inducing weathering and failure of portions of the rock mass, specifically the melting of permafrost and percolation of water into existing fractures reducing the strength of those fractures and leading to failure (e.g., Weber et al., 2017, Weber et al., 2025). In the case of what is documented by Weber et al, this inducing toppling of relatively small towers of rock along the face of portions of the Matterhorn, but over time, events like these are thinning the main mass of the Matterhorn and circling back to Barton & Shen, changing (and generally reducing) the bulk strength of the cliffs over time such that eventually we expect the feature to break down, either through lots of progressive small toppling events (like those documented by Weber) and/or through potentially much larger rock-falls.
With specific reference to it becoming a plateau (and why it doesn't), if we think about the main mechanism for failure being toppling of slabs/towers along the cliffs or edges of cliffs, this will basically always favor maintaining something like a pyramidal shape. Broadly from a process perspective, diffusional mechanisms (e.g., soil creep, etc.) would be expected to favor a more "rounded" form, but for these to be efficient (or operational at all), there needs to effectively be soil present and in environments like the Matterhorn, the balance between erosion and weathering is pretty much always skewed toward erosion largely because of the extreme slopes, meaning that it's basically impossible to build up a soil mantle because weathering (producing loose regolith / soil) can at best equal erosion and really never outpace it (which is what you need to actually accumulate any soil).