@Hungerburg raised a good point in the Rock glaciers tagged as moraines thread that rock glaciers may be tagged as “scree” rather than “glaciers” because the surface layer is rock rather than ice.
One of the main characteristics of a rock glacier is a surface layer of rock that insulates a layer of permafrost at the base of the feature. In many cases, this surface layer is accumulated from scree, talus, or glacial deposits such as moraines. We would mostly tag this as natural=scree in OSM, but some rock glaciers consist of rocks too large to be called “scree.” In this case, the currently undocumented and rarely used natural=boulders tag might be better.
I figured it would be good to survey current tagging for rock glaciers, and these are my results from Overpass today:
glacier:type=rock: 439 elements
+ natural=glacier: 436 elements
+ surface=scree: 103 elements
+ surface=snow: 7 elements
+ natural=scree: 3 elements
+ surface=ice: 2 elements
natural=glacier + surface=scree: 135 elements
glacier:type=* + surface=scree: 108 elements
geological=rock_glacier: 15 elements
+ natural=scree: 4 elements
That is not to suggest that any of the current tagging is correct or preferred, but just to look at what mappers have chosen to use previously when there has been little documentation.
Are there other tag combinations we should consider?