Early Holocene (>8500calBP) littoral sites are well documented along the Pacific coast of Chile north of 32°S, but they do not occur south of this latitude. It has been proposed that canoe Indians of Fuego-Patagonia, the earliest evidence for which is mid-Holocene (Punta Santa Ana; 7440calBP), adapted themselves to the sea from terrestrial hunter-gatherer populations already living since >13,000calBP in southernmost South America south of 52°S. This adaption may have taken place first in the area around Seno Otway, near the earliest maritime cultural sites, where transit to and from the interior pampas was relatively easy and forest providing trees for canoes existed. Seno Otway is also the proposed source for green obsidian, a distinctive lithic material found in many of the oldest maritime sites, including Túnel 1 and Imiwaia 1 along the Canal Beagle >300km to the southeast. This green obsidian was previously exploited and transported long distances by terrestrial hunter-gatherers, as evidenced by its presence in the Period III (9500-7400calBP) levels of Pali Aike and Fell's Cave located >200km east of Seno Otway. However, this obsidian does not occur in Period IV (after 7400calBP), when it and other obsidian types from distant sources are absent among the lithic tools found in these two sites. This hiatus in the long distant terrestrial transport of obsidian in southernmost Patagonia has been attributed to the catastrophic environmental effects of the H1 eruption of Hudson volcano (46°S) at ~7750calBP. This eruption, which was more than five time larger than the 1991 eruption of the same volcano, covered much of Tierra del Fuego with up to >20cm of tephra, and the Seno Otway area with at least >4cm of tephra. As well as interrupting long distance terrestrial transport of obsidian over all of southernmost Patagonia, it may have devastated for an extended time period the flora and fauna supporting the local terrestrial hunter-gatherers in this area, particularly in Tierra del Fuego, which was already isolated by the opening of the Strait of Magellan at ~9240calBP. Here it may have actually extinguished this culture completely. However, it was unlikely to have affected marine species. We propose that this volcanic eruption was a significant trigger to the development of the maritime population from the older terrestrial hunter-gatherers. © 2013 Elsevier Ltd and INQUA.