Soil microbial diversity has been studied mostly on already established soils, yet our knowledge of diversity in nascent soils is scarce. We studied the community of microbial colonizers in newly exposed volcanic deposits, which play an important role in the development of terrestrial ecosystems. Deposition of lava results in surfaces characterized by the lack of nutrients and water both of which represent a severe constraint for colonization and activity. This project addresses the relationship between the microbial community structure with soil chemical and physical properties. The microbial structure of Bacteria and Archaea communities was examined at a site in the Kilauea Caldera (Hawaii), by analysis of 16S rRNA gene sequences, Community-Level Phospholipid Fatty Acids, and Community-Level Physiological Profiles. Here we focused on a chronosequence of deposits ranging from 20 to 300 yr. Diversity was unexpectedly high, and mostly novel. Phylogeny of 16S rRNA gene sequences amplified from total DNA indicated the presence of various classes within the Bacteria domain and a high relative abundance within the Archaea domain of various unclassified non-thermophilic Crenarchaeota, with most sequences related to novel representatives. The Shannon-Weiner and Simpson's diversity indexes were higher for the oldest site and lowest in the youngest deposit, but vary among the in-between deposits. Biomass, richness, and diversity indexes paralleled carbon (%) and C/N ratio from soils. Carbon utilization profiles were site specific. In addition to unexpectedly high microbial diversity this study showed that microbial community is significantly different, and that overlap exists in community composition between deposits related by environmental variables. Our findings support the idea that bacteria are able to colonize and establish a community among recent volcanic deposits of mostly unknown species. This work yields new insights into survival and successional dynamic of microbes in extreme environments relevant for understanding both contemporary and ancient terrestrial systems.