Lower volcaniclastic rocks of Nisyros (22)

They occur on the western slopes of the volcano (Kardia site) as well as on the NE & E slopes of the caldera. A major part of the series is spread across the Kardia site. The base of the formation includes 4 beds of andesitic red scoriae, 5m thick each, mainly comprising lapilli with few blocks, 0.3-0.5m in diameter.

The third bed has been deposited through a pyroclastic flow mechanism while the remaining have been deposited by fallout.

A lapilli-tuff is subsequently observed, comprising ash and lapilli of gray-colored scoriae, a few basaltic andesite lava blocks and a significant percentage of limestone xenoliths (15-20%) 0,5-2cm in diameter.

It is markedly layered, some ash layers present wet flow structures and crossbeding.

A set of layers of ash from at least two eruptive events occurs on the NE & E slopes; these deposited gray-colored pumice as pyroclastic flow layers. These layers have been re – deposited on the upper members. Moreover, ash and lapilli tuffs appear at the eastern slopes; these lack the limestone xenoliths but are more abundant in andesitic lava blocks.

An alternating sequence of massive and stratified ash layers is noted here; impact sags are also observed.

The sedimentary structures of this lapilli-tuff led to the conclusion that the deposit was caused by the interaction between andesitic magma and excess surface water that resulted in building a series of tuff rings.

Several of these layers were subsequently re-deposited in the form of mud flows and debris flows.

Thickness reaches up to 60m.