As far as I can gather the eruption is in a valley - Geldingadalur (dalur = valley as in 'dale') - south of Fagradalsfjall (fjall = mountain, or 'fell') where the webcam is. Fagradalsfjall is an old shield volcano, 385m (1200') at it's highest point.

I think the hills in the picture are all lavas similar, perhaps contemporaneous, with Fagradalsfjall. The one opposite appears to have two layers, a harder top and a softer bottom in which rain has cut deeper crevices.

The pictures of sightseers give a better idea of scale:
https://grapevine.is/
(scroll down to the bottom articles)