Volenfell is the original name given to the region of Hammerfell. . It was named by the Dwemer, believed to be the Rourken Clan , who refused to sign a peace treaty with the Chimer .
Hammerfell's original name was Volenfell, named "City of the Hammer" by the Dwemer. Its ruins lay nearly submerged by the sands of the Alik'r.
The Ra Gada arrived in Volenfell in 1E 808 from the continent of Yokuda . Upon conquering the land, they renamed it Hammerfell. 
Volenfell is also the name given to the capital city of Hammerfell. The Dwemer called this city Volenfel, which meant "City of the Hammer."
Pocket Guide to the Empire.