6533b85dfe1ef96bd12bdbfa

RESEARCH PRODUCT

Vesiculated tuffs and associated features

subject

description

Vesiculated tuffs are tuffs that contain vesicles between the ash particles. Formation of the vesicles is the result of trapping of steam, the transporting agent of volcanic base surges, in wet, muddy or sticky ash deposited by the base surges. Vesiculated tuffs are described from various maars and tuff-rings in Europe (Iceland, France, Germany) and USA together with associated surface features such as: gravity flowage ripples, mud flow channels, current ripples, and current ridges. Other features described are: plastering of ash against obstacles and vesiculated accretionary lapilli, the latter containing vesicles in the outer layer. Vesiculated base surge deposits probably contained as much as 20–30% of interstitial water and fell out of the base surge clouds en masse owing to non-free flow and consequent accretion.