with minor, small lava flows and domes. The explosive eruptions produced pumice flows, bedded tuffs, debris flows, reworked polymict debris flows and lava flows less than thick. The porphyritic trachytes erupted at the summit of the shield and flowed towards the northeast and east. Because the porphyritic pyroclastic deposits are buried by younger volcanic rocks and glacial drift deposits, the maximum thickness of them is unknown. The felsic shield-building stage ended with the post-explosive phase. This phase of activity created small volcanic plugs, lava flows, minor pyroclastic flows, channelized debris flows and a few glassy dikes at the summit of the shield volcano. These consist of alkali-feldspar porphyritic quartz-trachyte and trachyte. Alkali-feldspar quartz-trachyte plugs formed in rhyolites and trachytes of the pre-explosive phase, as well as pyroclastic deposits and feldspar trachyte lava flows of the explosive phase. Later activity produced trachyte and phonolite plugs and lava flows. This volcanism occurred mainly at the shield's summit and on its western flank. Massive lava flows from this volcanic activity have a thickness of about while three successive lava flows at the summit have a combined thickness of more than . Lava from the western flank flowed over basement rocks and trachytes of the pre-explosive phase. In contrast, lava from the summit flowed over pyroclastic rocks and lava flows of the explosive phase. Mount Downton and Itcha Mountain were formed during this eruptive period. The final volcanic event of the post-explosive phase produced thick trachyte lava flows on the western flank. Mafic capping stage During the mafic capping stage, basanite, alkali olivine basalt and hawaiite erupted mainly from small parasitic cones, tuff rings and fissures in the eastern half of the shield. Eruptions occurred subglacially, subaqueously and/or subaerially as shown by a wide range in the degree of vesicularity, freshness and glass content of the lavas. In most cases, each parasitic cone produced three or four lava flows from breaches in the cone walls. These were erupted as pāhoehoe and ʻaʻā, but the tops of the lava flows are commonly missing due to erosion. Hawaiite was the most extensively erupted lava of the mafic capping stage, occurring mostly at the southern end of the Itcha Range but also in its interior. Volcanism of the mafic capping stage began with the eruption of aphyric hawaiite lava flows. These were extruded from dikes and dissected cinder cones in the central and southeastern parts of the