Lahar is a mudflow on the flanks of a volcano. It consists of mud and fragments of volcanic rocks plus any other available material. It is loose sediment and most examples photographed are recent. I want to demonstrate you a lahar that is hundreds of millions of years old (probably from the Carboniferous). It is a hard greenish rock resembling moderately altered basalt or andesite but it contains lots of clasts which are mostly volcanic but there is fair amount of limestone fragments as well.
Muddy matrix with volcanic clasts.
This lahar is exposed at the coast.
There are lots of clam shells.
Conglomerate boulder on top of lahar.
Pink clasts are limestone fragments.
Want to visit the place? Here are some guidelines. Go to Portraine (north of Dublin) and park by the sea in a parking lot with the following coordinates: 53° 29′ 22″ N 6° 05′ 56″ W. Go few hundred meters to the north/northwest.
This is my 200th post on Sandatlas.