This comparative work is based on study of pillow lavas sampled on six sites : (1) North-Atlantic Ridge at 36° N, (2) East-Pacific Rise at 13° N, (3) Ibléans Mountains (South-East Sicily), (4) Pre-Etnean lavas at Aci Castello (East Sicily), (5) Montgenèvre Massif (French-Italian Alps) and Arosa Zone (Graubünden, Swiss Alps). Samples of pillows from the modern ridges correspond to fresh lavas ("0 age"), the "Sicilian" lavas are more altered (Miocene-Pleistocene) and the "alpine" lavas belong to ophiolitic complexes (Upper Jurassic to Lower-Middle Cretaceous).

These comparative studies are concerned primarily with morphological aspects of the submarine effusive units. On the basis of observations of recent submarine flows via submersible, it has been possible to reconstruct the architecture and the eruptive processes of the older submarine sequences (Sicily, Alps).

The main factors controlling pillow morphologies and structures are : effusion rate, viscosity of the lava, flow velocity, local topography, and gravity. Pillow lavas from modern ridges and ophiolitic complexes are morphologically similar. Volcanic activity in these two cases is characterized by high effusion rates, attested to by the abundance of massive lavas, mega-pillows and vesicle-poor pillows. Sicilian lavas differ from the others by more rounded morphologies and portions of breccias and volcaniclastic materials. Volcanic activities were in the latter clearly more explosive, the high vesicularity of these sicilian pillows attest their setting in shallow water.

Brecciated units have been recognized in association with pillows at all sites. These units are the result of : lower lava supply rates, auto-brecciation, internal friction, hydromagmatism, and gravity.

In most of the studied areas, it was possible to observe and define volcanic edifices. These comprise a core with massive flows ("proximal" facies), grading vertically and laterally to elongated pillows then brecciated pillows, and finally accumulations of lava breccias due to a decreasing in the rate of effusion ("distal" facies). These volcanic piles have heights of several decameters to hectometers on modern ridges, the Sicilian volcanic sequences are of comparable size, but dismemberment diuring alpine tectonism limits observations inside the ophiolitic submarine constructions. [...]