Can subaerial pockmarks exist?

A new possible example of subaerial pockmark is shown. Recently, a question has been put foreward (Castellarin et al. 2006) as to whether the natural degassing of the Po plain sedimentary succession could originate morphological features such as marine pockmarcks (at least from the functional standpoint) in the present continental domain and, therefore, whether an analogy could be made with the hollows-clusters (suffusion phenomena) recorded on today’s emerged alluvial plains. However, in the two environments different geotechnical parameters and surface sediment conditions occur. The continental sediments are indeed fine, cohesive and unsaturated (close to the surface, at any rate) and cannot react mechanically like marine muds. Hence, subaerial environmental degassing may be favoured by various kinds and degrees of sediment permeability and by lower confinement pressure: these factors constrain the paroxystic character of gas uprising and seepage. The process could be the same in both environments, and its morphological expression alone might differ: the name alone could be lacking. If the mentioned examples are reliable then they could indicate very peculiar and unusual local environmental conditions for subaerial sediments. Nonetheless, they are evidence of the ancient age of these phenomena and state their independence from human activities.