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Adagdak reported activity




Event Name : Adagdak Older Cone

Start: 2200000 (± 370000 Years) Years BP Ar/Ar

Lava flow: BibCard
Tephrafall: BibCard
Cone: BibCard
Eruption Type:Explosive
Eruption Product: andesite BibCard
Eruption Product: andesite BibCard

Description: From Baten (2002): "Mt. Adagdak (650 m asl) was built from three stages of volcanism (Figure 1.5 [in original text])."

"The second stage of volcanism resulted in the formation of two composite cones. The older cone formed on the southern portion of the remnant shield and the younger cone formed on the eroded northern flank of the older composite cone (Coats, 1956). Both cones are primarily andesitic in composition."

"...the older cone yields an 40Ar/39Ar date of 2.20 +/- 0.37 Ma (2 sigma error)..."

From Meyers and Frost (1994): "A prominent break in slope on the southern flank marks the base of an older composite cone formed on top of the earlier shield. Like the latter, this volcanic structure was severely affected by marine erosion and cut back nearly to its center."

From Coats (1956): "Older composite cone-Viewed from the south, the long, gentle grass-covered slopes of the shield volcano that forms the substructure of Mount Adagdak are seen to be crowned by the steep, relatively smooth, bare slopes of a wide, low cone. The break in slope occurs at altitudes ranging from 800 to 1,000 feet; the smooth slopes of the upper cone are locally broken by crags developed on small lava flows. This cone represents an older composite cone of Mount Adagdak. It consists largely of lapilli-tuff beds, but includes subordinate lava flows and necks of hornblende andesite. This material accumulated first ns a cone about 800 feet high, the sides of which arc as steep as 26', on the top and the deeply eroded northern flank of the shield volcano. A later explosive episode, centering about a vent northwest of the earlier one, produced an inner, concentrically nested crater, the summit of which was as much as 1,920 feet in altitude, about 200 feet higher than the outer rim. The time interval between the formation of the two craters was probably very short."

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Page modified: March 30, 2017 14:36
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