They are different volcanoes.  I unfortunately haven't got a photo of Hlöðufell to upload but here's a link to one: .  I can't seem to find a decent map of Iceland online, but Hlöðufell is southwest of Langjökull and Herðubreið is north of Vatnajökull (just northeast of Askja).  I would think that Herðubreið is considered Iceland's most famous tuya and I haven't heard any such sentiment about Hlöðufell.  Neither of the names mean tuya, but I think the best translation of tuya might be Búrfell (which name many Icelandic mountains possess).  Best regards,