Small depressions that appear alongside your foundation walls or near concrete slabs and stairs are mainly caused by poor soil compression and water erosion. If the void is caused by downspouts terminating too close to the foundation, consider extending the downspouts with ADS piping.
If downspouts do not seem to be the cause, the best action you can take is to simply fill the void to keep it from getting bigger. First, remove any yard waste or trash that may have become trapped in the hole. Next, fill the hole with soil.
One mistake some people make is to fill with gravel first, then soil on top. Gravel allows water to flow, and the void could continue to grow under a layer of gravel. Filling the hole completely with a clay/topsoil mix will do a good job and can add the stability needed to keep the void from reforming. Most importantly, tamp the “fill” until it is level with the surrounding soil, or just a bit higher, perhaps, to allow for some continuing natural soil compaction.
Finally, check to see that the soil along your foundation allows for water to flow away from the house to avoid obvious problems with water infiltration into the basement or crawl space.
