As throughout Ireland, much erosion has taken place in the intervening time and at some point, likely in the last 11,700 years which is known as the Holocene (since the end of the last Ice Age) this section of the headland became a bridge with a sea cave eroded through it and then subsequently it became detached from the mainland behind it.
Thus forming what we see today, an impressive sea arch which is Ireland's largest sea arch. Note that a sea stack, such as Dun Briste is different to a sea arch.
It is a difficult photograph to shoot a landscape like this contre-jour but the movement and colour in the sky, coupled with some good post-processing has resulted in a fine image that is in contrast to shooting with the sun and its clear light (image coming soon in a subsequent post).
Making use of the texture and feeling of this deserted Irish beach at sunset.