He saw the road rise steeply off into the distance.
No, steep is not an adverb. This is an adjective and occasionally a verb.The adverb form is steeply.
mountain
Mountain
the coastline?
The Zambezi River
Steeply? a cliff maybe?
a slip face
mountain
i think is hill
This ridgeline rises steeply to a much higher altitude.
a waterfall