wild slope readings on 90m DEM!

[bananpud7]

Hey everyone, we're hoping someone can help me figure out a weird issue we're having with some DEMs.

So, we're working with three different DEM resolutions for the same area, which are 30m, 90m, and 1km.

The elevation data itself looks pretty similar across all of them, only about a 2meter difference, which seems normal.

But here's where it gets wild, when I calculate the slope in percentage (using raster > analysis > slope), the numbers are all over the place!

the 30m DEM maxes out at 192, and the 1km DEM is around 33.85.

Totally expected. But then the 90m DEM is showing a ridiculous maximum slope of 9641!

We're completely stumped on what could be causing such a huge, outlier number for just the 90m one.

Has anyone ever seen something like this, or have any ideas what might be going wrong?

 

[Krajsis1]

I have two potential solutions for this. Look for no data values or artifacts and see if you can clean those up or maybe reclassify them which could help with the slope calculation. You can also try to resample the 90m dem to a higher resolution and then calculate the slope to see what kind of values you get.

 

[Carbguy]

Most likely culprit?, you've got a spike or dip i.e., a no data cell, bad pixel, or interpolation artifact in that 90m raster, if the slope tool hits a sudden elevation jump between adjacent pixels, especially if one is 0 or nodata, it can spit out a wild value like that