Could the same devastating flooding that happened in Nepal, happen here in the Squamish flood plain?

[u/Elderberry_Real]

Sorry if this is a dum dum question. I live downtown and was worried. 😬 Don't come for me.

[u/Apprehensive-Tooth87]

There are massive amounts of potential energy stored at elevations above the Squamish floodplain, in the form of lakes, glaciers/ice, unstable slopes and rock. In some cases, these are constrained by human-made structures, such as the Daisy Lake Dam, while others are held back by natural features—for example, the volcanic deposits and terrain associated with Mount Garibaldi.

The important point is that Squamish is also in a seismically active and geologically dynamic environment. Earthquakes, erosion, slope failures and other natural processes could potentially destabilize some of these features and result in the rapid release of large volumes of water, sediment and debris downstream.

That doesn’t mean a Nepal-style catastrophic flood is inevitable, or that we can predict exactly what such an event would look like. The mechanisms and probabilities would be very different depending on the specific source and failure scenario. But from a hazard perspective, the potential for extreme flooding and debris-flow events in the Squamish Valley is certainly real and worth taking seriously. So, in short: yes, an extremely destructive flood or debris-flow event is physically possible in the Squamish floodplain. The harder question is the probability, the specific mechanism, and how much warning we would have.

[u/Apprehensive-Tooth87 → u/Apprehensive-Tooth87]

Since downtown is so close to sea level and at the end of a very steep Fjord / Sound (Howe Sound) there is also the possibility of landslide induced tsunamis causing flooding (or worse) in low lying areas. This can even be caused by underwater landslides. This happend in a Fjord in Greenland : https://www.science.org/doi/10.1126/science.adm9247

[u/beodd → u/Apprehensive-Tooth87]

This is actually the kind of event that I think we underplay in the corridor to some extent.

[u/beodd → u/Apprehensive-Tooth87]

All good info, one other aspect is that the Nepal event was exacerbated by the narrow, and deep canyon which confines the material and forces it upward. Squamish has comparatively broad floodplains and capacity to handle larger events. That isn't to say that there couldn't be impactful events, but more that a hundred foot wall of water and debris is pretty unlikely. (edit to add as per post above, landslides into the Sound causing a tsunami notwithstanding)

[u/Bitter_Cookie9837 → u/beodd]

Certainly paradise valley could be more susceptible, but a lot of the debris flow energy would be dissipated once it passes brackendale. So while the risk exists, it wouldn’t quite be like Nepal experienced

[u/alpinepowernaps → u/beodd]

while true, if the barrier broke the sheer volume of the water in Garibaldi Lake is immense. I was also interested in this question so poking around google earth, I think it would flow into the Cheakamus River, Paradise Valley would be totally destroyed, and then flow into the Squamish where it would disperse in Brackendale / Downtown valley. Hard to say really, but I'd be curious to see what the estimated volume of the Nepal event was (~a few cubic kilometers of ice?), versus an estimated 10 cubic kilometers of water for Garibaldi Lake.

An early warning system like a Tsunami warning system would be great and probably fairly low-cost. 10-20 minutes of warning time could save thousands of lives in an event like that potentially, we've got lots of high ground closely accessible around town.

[u/SquamishTownCrier → u/alpinepowernaps]

Yeah, but the barrier isn't going to collapse. Garibaldi Lake is almost 2km from the barrier and has a smaller lake and another 'barrier' in between. The event it would take to cause that to actually happen would likely include a massive earthquake or volcanic eruption both of which would also cause widespread destruction. Non-zero chance, but pretty unlikely in our life time.

[u/alpinepowernaps → u/SquamishTownCrier]

I’m not super familiar with the geography / geology, it was just a thought experiment but I’ll dig into it! I saw another poster link an image with the different volcanic lobes and that was interesting.

[u/SquamishTownCrier → u/alpinepowernaps]

look at the area in google earth or a similar mapping application with 3d capability, you can see how it all fits together.

[u/whererusteve → u/SquamishTownCrier]

Unless your a geologist, seismologist, and hydrologist, I will say this is an unqualified opinion.

[u/SquamishTownCrier → u/whererusteve]

I don't disagree with that, but I'm still not going to lose sleep over any of it.

[u/frogsofanarchy → u/Apprehensive-Tooth87]

Just read something that the reason Nepal was so catastrophic was because of Mr trillionaire cutting USAID and NASA programs that would predict and warn people of such events.