Þorbjarnarfell was formed in one eruption, but due to how fractured it is one would conclude that multiple events formed its appearances, most of which were caused by faulting.
Þorbjarnarfell hefur því myndast í einum atburði, en sökum þess hversu brotið fellið er má álykta að margir atburðir hafi stuðlað að útliti þess.