Description: The Hayes tephra set H has a complicated history of nomenclature, tephra name aliases include the Jarvis Creek Ash (Reger and others, 1964), Cantwell Ash (Bowers 1979), Watana (upper oxidized and lower unoxidized) tephra (Dixon and Smith, 1990), and Tangle Lakes Tephra (Beget and others, 1991).
From Riehle and others (1990): "The most widespread of all Holocene tephra deposits in the Cook Inlet region of south-central Alaska is a set of deposits from Hayes volcano. Because of their unique phenocryst content-biotite in rare amounts and a high proportion of amphibole to pyroxene-the deposits are readily identifiable at all but the most distant sites where they are very fine grained...The set originated at Hayes volcano in the Tordillo Mountains 150 km northwest of Anchorage: seven or possibly eight closely succeeding deposits, low-silica dacite in composition, compose two main lobes that extend northeast for 400 km and south for at least 250 km from the vent. We estimate the total tephra volume to be 10 km 3; multiple layers imply four to six larger and two or three smaller eruptions."
From Beget and others (1991): "The geochemistry, petrography, and distribution of the Jarvis Creek Ash (Pewe 1965, 1975a) indicate that this tephra from the lower Delta River area of central Alaska is correlative with volcanic ash from sites in south-central Alaska near Tangle Lakes (upper Delta River area) and the Cantwell ash from Hayes volcano found in the upper Nenana River area (Riehle and others, 1990). Volcanic glass compositions of distal Jarvis Creek and Tangle Lakes tephra samples are compositionally restricted, while several discrete glass populations are present in some Cantwell samples collected nearer Hayes volcano. These correlations extend the known distribution of Hayes volcano tephras across the Alaska Range and into central Alaska, a distance of more than 650 km."
Riehle (1994) proposed, "...that the group of beds be informally referred to as Hayes tephra set H (for Hayes River Pass, the site of the reference samples). As previously applied to the Hayes deposits (Riehle and others, 1990), a set is two or more closely succeeding tephra deposits that are chemically or mineralogically similar (Mullineaux and others, 1975). The designation "H" allows for future recognition of other tephra sets. The name "Hayes tephra set H" emphasizes source (consistent with NACSN, p. 851) and implies that each deposit is part of a group which has a wide geographic extent."
From Wallace and others (2015) [Hayes Volcano proximal reference study]: "Tephra fallout, eolian silt deposits, and buried soils make up the uppermost two meters of the Hayes River exposure at site 11HYKLW001 (figs. 1B, 2 [in original text]). Tephra deposits generally correlative with tephra set H are exposed ~1 m below the surface and consist of 10 tephra-fall layers distinguished by variations in particle size, bedding, color, or separation by buried soils (figs. 5, 6 [in original text])...Individual tephra layers range from 1-40 cm thick. On the basis of thickness, grain size, and proximity, eight of the ten tephra-fall deposits were probably erupted from Hayes Volcano (31 km)...Tephras F and H are sufficiently thick to be sub-sampled to test for compositional variation. Six buried soils are evident in this section and all but one were sampled for radiocarbon dating."
"Tephra B (AT-2559) is a non-oxidized, clean, salt-and-pepper colored tephra that contains bright white dacite pumice with rhyolite matrix glass (72.8 weight percent SiO2; table 5 [in original text]). Pumices are highly inflated, glassy, and contain phenocrysts of plagioclase, amphibole, and Fe-Ti oxides in clear microlite-free matrix glass (fig. 7G [in original text]). Plagioclase phenocrysts are notably fritted, or "sieved" (fig. 7H [in original text]), more so than in other tephras in the sequence. Although point count data on pumice grains were not collected because of the small grain size, the pumice grains are relatively crystal poor yet the deposit contains abundant glass-coated free crystals.Rare (<1 percent) biotite grains are observed in all size fractions and exhibit both euhedral and irregular forms. Mafic mineral counts suggest a high amphibole to pyroxene ratio (table 3, fig. 8 [in original text]). Because of the highly vesicular glass, locating areas large enough to analyze by microprobe was difficult."
"Tephra D (AT-2567) is dominated by dense, light-medium gray, fresh-looking lithic grains and minor cream-white pumice which impart an overall medium gray color to the deposit in wet and dry samples (fig. 6 [in original text]). The lithic grains and pumice contain phenocrysts of plagioclase, amphibole, and Fe-Ti oxides. Lithic grains have grayish microlite-rich matrix glass (not analyzed) while the pumices have clear rhyolite matrix glass (73.6 weight percent SiO2) (fig. 7I [in original text]). Rare (<1 percent) biotite grains are observed in all size fractions and exhibit euhedral and irregular forms. Mafic mineral counts suggest a high amphibole to pyroxene ratio (table 3, fig. 8 [in original text])."
"Tephra E (AT-2565) is dominated by dense, light-medium gray, fresh-looking lithic grains and minor cream-white pumice, which impart an overall pale yellowish brown color to the deposit in both wet and dry samples. The lithic and pumice grains contain phenocrysts of plagioclase, amphibole, and Fe-Ti oxides (fig. 7J [in original text]). The lithic grains have grayish microlite-rich matrix glass (not analyzed) while the pumice grains have clear microlite-rich matrix glass that is rhyolitic in composition (72.7 weight percent SiO2) (table 5 [in original text]). Biotite is very rare in this sample and only a few grains were observed. Mafic mineral counts suggest a high amphibole to pyroxene ratio (table 3, fig. 8 [in original text]). Despite being microlitic, pumice glass in this sample is fairly easy to analyze with the electron microprobe."
"Tephra F is 40-cm thick and was subsampled into two parts, (A) the coarse-grained bottom 10 cm (tephra F1, AT-2560), and (B) the finer-grained upper 30 cm (tephra F2, AT-2561) to assess compositional variation (figs. 5, 6 [in original text]). The overall deposit color is very pale orange. Both samples contain cream-white dacite pumice (WR, 63.8 weight percent SiO2) with mostly microlite-free rhyolitic matrix glass (71.3-74.1 weight percent SiO2) (tables 4, 5 [in original text]). Glass composition within the upper unit (tephra F2) appears to have higher silica content (74 percent SiO2) compared to the lower section (tephra F1, 71-72 weight percent SiO2). Minor amounts of dense, light-medium gray lithic grains are present but were not analyzed. Pumice >0.250 mm tends to be more oxidized and have a pale yellow brown color while smaller grains (< 0.125 mm) tend to be pure white. Both pumice and lithic clasts contain phenocrysts of plagioclase, amphibole, and Fe-Ti oxides. Rare (<1 percent) biotite grains are observed in all size fractions and exhibit euhedral and irregular forms, including large grains as much as 2 mm in diameter. Mafic mineral counts suggest a high amphibole to pyroxene ratio (table 3, fig. 8 [in original text]). Despite the glass being mostly microlite free, some grains are highly vesicular, making glass analysis difficult (figs. 7K, L [in original text])."
"Tephra G (AT-2562) is dominated by dense, light-medium gray, fresh-looking lithic grains with minor cream-white pumice, which impart an overall medium gray color to the deposit in wet and dry samples (fig. 6 [in original text]). The matrix glass of the pumice is bimodal high-silica (74.6 and 77.8 weight percent SiO2) rhyolite (table 5). Both lithic and pumice grains contain phenocrysts of plagioclase, amphibole, and Fe-Ti oxides. The lithic grains have grayish microlite-rich matrix glass, whereas the pumice grains have microlite-free clear glass and microlite-rich grayish glass. Rare (<1 percent) biotite grains are observed in all size fractions and exhibit both euhedral and irregular forms. Mafic mineral counts suggest a high amphibole to pyroxene ratio (table 3, fig. 8 [in original text]). Pumice clasts are generally highly vesicular and the sample is difficult to analyze by electron microprobe because the threads of glass are narrow and microlite-bearing (figs. 7M, N [in original text])."
"Tephra H is 20-cm thick and was subsampled into 2 parts, (A) the coarse-grained bottom 10 cm (tephra H1, AT-2563), and (B) the finer-grained upper 10 cm (tephra H2, AT-2564) to assess compositional variation (fig. 5 [in original text]). Unit H contains grayish orange oxidized pumice, which imparts a dark yellowish orange oxidized color to the deposit in wet and dry samples (fig. 6 [in original text]). A minor amount of dense, light-medium gray lithic material is present in this sample but was not analyzed. The pumice matrix glass is clear, microlite-rich, and vesicle textures are generally fluidal (fig. 7O, P [in original text]). Glass from the lower part of tephra H (H1) is bimodal with nearly subequal populations of dacite and rhyolitic (65 and 75 weight percent SiO2) while glass from the upper part of tephra H (H2) has an entirely rhyolite composition (75.3 weight percent SiO2). Rare (<1 percent) biotite grains are observed in all size fractions and exhibit euhedral and irregular forms. Mafic mineral counts suggest a high amphibole to pyroxene ratio (table 3, fig. 8 [in original text]). Despite the glass being microlitic, this sample is fairly easy to analyze on the electron microprobe owing to the relatively large areas between vesicles."
"Tephras B, F, G, and H of Unit III, as well as the underlying Units I and II, are the most significant and distinctive deposits of the Hayes River outcrop and are the most likely to represent widespread deposits in south-central Alaska."
"On the basis of major-element glass compositions (fig. 10 [in original text]), we find that the Jarvis Ash Bed correlates most closely with our tephra F, which is the thickest tephra at the Hayes River outcrop (40 cm), and the only tephra that contains medium (4-16 mm) lapilli (fig. 16 [in original text]). This may be consistent with the conclusions of Riehle and others (1990), who indicated that tephra G at site 23 was deposited from a northward-directed ash cloud that would have travelled over interior Alaska."
"Combellick and Pinney (1995) describe a 3-cm-thick tephra on the Kenai Peninsula dated at 3,530+/-70 14C yr B.P. They conclude, on the basis of major-element glass chemistry and minerology, that it correlates with unit A of Riehle (1985), the uppermost tephra at his site 23 (table 9, figs. 8, 10 [in original text]). The glass composition of this tephra is most similar to our tephra H, which is also the uppermost tephra at the Hayes River outcrop (fig. 10 and 16 [in original text])."
"The Watana tephra has a distinctive upper oxidized component and lower non-oxidized component in subaerial exposures, and as many as three discrete layers in a lake-sediment core. The tephra ranges in thickness from 6-20 cm, and has an age within the range of 2,830-5,270 14C yr B.P. based on radiocarbon ages of numerous paleosols bounding this layer in the Susitna River valley (J.E. Dixon and others, written commun(s)., 1985; Dilley, 1988)."
From Mulliken (2016): "Stratigraphically, the Watana tephra is separated into an upper and lower component, and there has been some question as to whether the deposit represents a single or multiple volcanic events (Dixon and others 1985). Glass geochemical analyses demonstrate that the deposit is relatively homogenous despite differences in oxidation and color. Similarity coefficients calculated between mSRV Watana reference tephra samples and proximal Hayes Volcano reference samples suggest that the Watana tephra is correlative with the Hayes tephra set; however, most archaeological samples were taken as bulk Watana tephra samples, rather than as separate samples from the oxidized upper and unoxidized lower components of the tephra, which complicates correlation efforts. Specifically, Watana tephra samples correlate, with similarity coefficients greater than 0.95, to Hayes River Outcrop tephras D, E, F2, H (H1 and H2) of Wallace and others (2014). Proximal tephras F and H represent eruptions large enough to have been deposited distally; the two samples of unoxidized portion of the Watana tephra have high similarity coefficients with proximal tephra F2, which is also unoxidized, whereas the two samples of the upper oxidized portion of the Watana tephra have high similarity coefficients with proximal tephra H, which is also oxidized."
"These results suggest that the Watana oxidized/unoxidized tephra couplet represents proximal tephras F and H of Wallace and others (2014) (Figure 6.1 [in original text]). Proximal tephra F2 is unoxidized and is represented as the unoxidized portion of the Watana tephra in the mSRV, whereas oxidized proximal tephra H is represented as the upper oxidized portion of the Watana tephra in the mSRV. Indeed, archaeological investigations have occasionally noted eolian units or thin paleosols between the upper and lower portions of the Watana tephra, suggesting the deposit represents two volcanic events separated in time (Dixon and others 1985; Romick and Thorson 1983). Schiff and others (2008) also note two tephra beds in Bear Lake, south of Hayes Volcano, likely originating from Hayes Volcano (based on the presence of biotite), separated by 1.5 cm of gyttja and with a modelled basal age of 3940-4120 cal yr B.P. Bayesian models of calibration produced as part of this study suggest that deposition of proximal tephra F/unoxidized Watana and proximal tephra H/oxidized Watana could have occurred in rapid succession or been separated by a maximum of 380 years."
The Global database on large magnitude explosive volcanic eruptions (LaMEVE; 2017) reports a magnitude of 5.400, bulk eruptive volume of 8.100 cubic km and a dense rock equivalent eruptive volume of 1.000 cubic km for the eruption.