From Wood and Kienle (1990) 
: "Yantarni volcano is an andesitic stratovolcano comprising ~3.5 cubic km located adjacent to, and within the same arc segment as, Mount Chiginagak. The volcano was not discovered until 1979, owing to its modest summit elevation, remote location, and lack of documented historic activity. Its name is taken from the adjacent bay, named on a Russian chart as "Z. Yantarni" for amber purportedly found there. First mapped at a 1:250,000 scale, the volcano has since been mapped at 1:63,360 and its eruptive history and chemistry determined in greater detail.
"The volcano formed near a high-angle fault at a site of previous Tertiary magmatism. The current cycle of eruptive activity began in middle Pleistocene time with extrusion of andesitic lava flows, perhaps from multiple vents. By the late Pleistocene, central-vent volcanism had initiated construction of a small stratovolcano. The cone was breached in late Holocene time (between 2,000 and 3,500 yr ago?), forming a debris-avalanche deposit which was possibly accompanied by a directed blast and closely followed by emplacement of a dome and pyroclastic flows. The pyroclastic flows are about 1 cubic km in volume and extend 4 km down-valley.
"Disequilibrium phenocryst assemblages, a lack of correlation between phenocryst assemblages, and whole-rock compositions, eruption of different compositions of magma in close succession, and the small volume of eruptive products suggest Yantarni is an immature volcano lacking a large, shallow magma chamber."