Event Name : Moffett Intermediate Ash
|Start: 6960 (± 100 Years) || Years BP C-14 (raw) || |
|Stop: 4460 (± 180 Years) || Years BP C-14 (raw) || |Description:
|Eruption Product: || andesite ||
Waythomas and others (2003) tentatively identify Moffett Volcano as the source of the Intermediate Ash, observed on Adak Island and also called AD-4 by Kiriyanov and Miller (1997).
From Kiriyanov and Miller (1997): "AD-4 ash is 4-8 cm thick and consists of pumice gravel and lapilli with a maximum size of 3 cm, small amounts of gray clay- and silt-size materials and fine-grained sand, and a large amount of rock fragments 0.5-0.8 cm in size. The coarser material is concentrated in the middle of the ash layer. Distinctive features of this ash are a considerably large amount of rock debris (13%), absence of pyroxenes, and a very small content of green and brown hornblendes (1-2%). The inferred age of the ash is 4500-4600 14C years (Table 1 [in original text])."
From Okuno and others (2012): "The lntermediate tephra-fall deposit consists of pumice and lithic fragments with a cross-laminated ash bed. It is 43cm thick and contains a large amount of dense lithics with a maximum size (ML) of 3.8cm."
From Waythomas and others (2001): "A thick lapilli tephra deposit about the same age as the Intermediate Ash is present at locality 00CW06 northeast of Kanaga Volcano (fig. 9 [in original text]) but is not recognized elsewhere on Kanaga Island. Radiocarbon ages associated with Kanaga Island tephra T7 match those of the Sandwich Ash (fig. 13 [in original text]); however, the T7 deposits consist of massive sand-size felsic tephra with granule-size juvenile lapilli at the base (sec. 99CW75, fig. 9 [in original text]) or a single thin lapilli bed (sec. 99CW83, fig. 9 [in original text]) and do not exhibit the sequence massive gray fine ash/oxidized granule lapilli/massive gray fine ash that characterizes the Sandwich Ash on Adak Island. Thus, we are uncertain whether tephra T7 and the Sandwich ash are the same tephra deposit..."