A large area of soil, approximately 50 meters by 60 meters has slid down a bank towards a river during the heavy rainfall in late 2015 that caused flooding in the northern part of the UK. The slide was of at least a meter in some areas and in others perhaps 5. The depth of soil that has moved was suspected to be several meters deep. There is a shale layer above a clay layer and the former seems to have slid over the latter.
We had been called in to clear an access for land surveyors to assess the ground. Other staff were also digging bore holes to inspect the soil bellow ground in numerous areas. This latter operation was sending vibrations throughout the area.
With the trees that have followed the landslide in their entirety (as the majority of their roots are only in the top meter or so) still standing and alive, it was impossible to assure that they were not a risk to the persons working around them.
We therefore deemed the area unsafe and removed the most obviously potentially dangerous trees near the area where people would be working. Some of the trees had been observed tilting whilst the workmen were on site and these (and others) had the area up to 1.5 meters away from the base of the trunk lifting/tearing away from the ground.
It was very interesting to see this as it is not something I have come across before and wonder how one could properly inspect the damage done to the tree roots. Many of the roots will have been severed and as it has not been very long since the event, circa 8 months, decay will not have set in fully. I expect a few more of these trees will fall down in the next few years.
Many of these trees are white poplars though there are some sycamores, beech and ash in the area as well.
The sycamores that have landed in the river are obviously dead, most probably from oxygen starvation with the roots being entirely submerged rather than, or in addition to, direct physical damage as again, these are still standing. They have tilted further since our first visit.