I am not sure if the Hnubbafossar or Tungnaárfellsfoss still exists due of a power plant next to the waterfall. But if the river Tungnaá still flows at Hnubbafossar it one of the most unique waterfalls in Iceland, specially when the flow in the river is low.
The river Tungnaá gushes down a lavafield creating numerous small waterfalls over a wide of 500 meters. I don’t think the small fall are very high, I guess appr. 5-15 meters.
The Hnubbafossar can be found 2 km from road F-208 by Tungnárfell, between Sigalda and Landmannalaugar in the South of Iceland. From road 26 you have to take the exit to road F208 and drive to the south until you reach the river Tungnaá.