12 December 2023
Spring is landslide season in Pittsburgh. Iciness is a superb time to get in a position for it and there’s no time like the existing. With local weather alternate expanding Pittsburgh’s rainfall and downpours, our dissolve-in-water bedrock is getting moist quicker.
This morning the Pittsburgh Submit-Gazette reported that, because of a $10 million federal grant, the Town of Pittsburgh is ready to start out two landslide mitigation initiatives alongside town streets on Mount Washington and is hanging a 3rd one out to bid.
Fortunately there may be cash, even though now not a large number of it, for municipalities to forestall landslides on our roads, however for those who reside above a landslide and also you personal the land that slid you’re out of success. The slide in the end takes your own home with it.
Pittsburgh is particularly vulnerable to landslides as a result of our geology.
Two herbal stipulations happening in western Pennsylvania are maximum accountable for landslide issues all over the realm. First, in lots of puts the bedrock is composed basically of shales and claystones. The principle perpetrator is a thick, 40- to 60-foot rock layer referred to as the Pittsburgh purple beds.
[Red bed]rock all of a sudden falls aside in water and has a tendency to lose energy with every seasonal freeze-thaw and wet-dry cycle. Water that collects within the rock has little probability to empty and due to this fact is helping make the slope risky from the interior out.
The second one naturally happening situation accountable for landslides is western Pennsylvania’s panorama, which is ruled by way of steep hills and valleys.
[Hillside] soils usually are stiff however very vulnerable to downhill motion. This motion usually is imperceptibly sluggish. All over the spring, then again, the soil incessantly turns into very moist from thawing snow and spring rains and the creeping can boost up right into a full-blown landslide.
— Pittsburgh Geological Society: Landsliding in Western Pennsylvania
It’s simple to search out purple mattress outcrops on our hillsides. Right here’s one in Schenley Park the place there was once topsoil however the purple mattress, previously underneath the skin, eroded and left this tree on stilts.
A better have a look at the purple mattress rock displays that it broke into tiny items — little crumbles — when it were given moist. My foot is within the photograph for scale.
The site of those pictures is marked on a Google topo map of Schenley Park beneath. Realize how steep the hillside is the place the purple mattress is uncovered. Uh oh!
As a result of the superiority of Pittsburgh purple mattress rock there are landslide issues all over Allegheny County. Click on right here or at the map symbol beneath to look the main points. Understand that the colours purple and orange are unhealthy. The one secure colour is yellow.
And only for emphasis, take a look at this video of a space that slide down the hill in 2019.