Grain size, areal thickness distribution and controls on sedimentation of the 1991 Mount Pinatubo tephra layer in the South China Sea

Bull Volcanol (2004) 8:226–242

In the original publication of this article, Figs. 1, 2, 4, 5, 6, 8, 9 had not been reproduced correctly due to technical problems. We apologise for this mistake.

The correct versions of these figures can be seen here.

Fig. 1.

Thickness contours (in mm) of the June 15, 1991 Mt. Pinatubo ash fall deposit in the South China Sea (isobaths in m) and on Luzon Island (unlabeled isopach is 200 mm). On-land thicknesses (layer C) were taken from Paladio-Melosantos et al. (1996) and E. Listanco (unpublished data 1991). Marine core sites are denoted as follows: circles R/V Sonne cruises SO-132 in 1998 and SO-140 in 1999 (this study); triangles SO-95 in 1994 (Wiesner and Wang 1996); squares SO-114 and R/V Ocean Researcher 1 cruise OR-455, both in 1996 (Kuhnt et al. 1996; Wiesner et al. 1997; Wang 1999); pentagons SO-115 in 1996/1997 (Stattegger et al. 1997); diamonds 1997 cruises of R/V Explorer (F. Siringan, personal communication 1998); inversed triangles 1998 cruises of R/V Xiangyanghong-14 (R. Chen, personal communication 1999); cross 1990–1992 sediment trap mooring station SCS-C (Wiesner et al. 1995). Filled symbols ash thickness measured; half-filled symbols ash observed, thickness not reliable due to core disturbance or postdepositional redistribution; open symbols no macroscopically visible ash. Numerals at core sites refer to those tephra sections that were analyzed by sieving/pipetting and correspond with the last two digits of the station labels given in Table 1 and Figs. 3, 4, 5, and 6

Fig. 2.

Velocity-height section of mean zonal (solid line) and meridional (dashed line) winds on June 15, 1991, combined with the timing and plume top altitudes (bold curved line) of the June 15–16 Pinatubo eruptions. Wind velocities were obtained from ECMWF ERA-40 reanalysis data sets (for reference, see European Center for Medium-Range Weather Forecasts 2000) and averaged over the area 10.25°–18.75°N, 109.25°–120.25°E; positive (negative) values indicate westerly (easterly) flow for the zonal component and northerly (southerly) flow for the meridional component. Chronology of eruptive plume events was adapted from Holasek et al. (1996)

Fig. 4.

Thickness contours (in mm) of a unit I (unlabeled isopach is 50 mm) and b unit II (*combined with the single ash layer to show the total distribution of fine ash). Core site symbols are as in Fig. 1 but filled where the boundary between unit I and II is sharp, half-filled where boundary is gradual, and open where no boundary is present. Numbers in italics at core sites are mean grain sizes (in φ-units) for the particle populations <9φ. Values were obtained by the Laser method and converted to sieve/pipette particle means on the basis of the equation given in the section on Sampling and Methods (bracketed values denote sites where contamination of the ash section by particles from above and beneath was difficult to avoid during sampling). Bold dashed line represents the bulk ash lobe axis (see Fig. 1)

Fig. 5.

Downwind variations in a thickness, b maximum clast size, and c median diameter of the submarine Mt. Pinatubo tephra layer and its stratigraphic units as a function of distance from source along the bulk ash dispersal axis. Short-dashed thickness line in a indicates diffuse contact between unit I and II. Bracketed data in b and c refer to core sites located south of the lobe axis (their source distance was orthogonally projected onto the center line; see Fig. 1 for core positions). Note that stations 132-37, -28, -29, -13, and -14 plot along a line which connects the thickness maximum of unit II with the one of the distal ash layer (cf. Figs. 1, 4)

Fig. 6.

Bulk ash grain size distributions of the submarine Mt. Pinatubo tephra layer at increasing distance downwind along the main dispersal axis. Also shown is the percentage of ash in the >9φ size range as a function of distance from source. Size spectra of unit I (open bars) and unit II (black bars) are stacked and normalized to the bulk ash deposit on the basis of unit thickness and unit bulk density (averaging 1.3 and 1.1 g/cm³, respectively); grey bars single ash layer. Note that at station SO-132-13 unit I was too thin (1 mm) to be analyzed separately by sieving/pipetting; also note that the distal station SO-132-05 is positioned south of the center line (cf. Figs. 1, 5, 6)

Fig. 8.

Logarithm of thickness versus square root of isopach area for the June 15, 1991 Mt. Pinatubo ash-fall deposit along with two straight-line approximations for the isopach ranges 30–1 cm (T₁ and T₂) and 30–0.1 cm (T₁ and T₃) (see Fig. 1 for data source). Open symbols denote isopachs that could not be closed with confidence. Inset lists the regression equations for T₁, T₂, and T₃. Numerals in boxes are bulk volumes in km³ calculated for the two straight-line segments T₁-T₂ and T₁-T₃ according to the method of Fierstein and Nathenson (1992). T_max is the extrapolated thickness at the vent; b_t1, b_t2, and b_t3 are the thickness half-distances for the segments T₁, T₂, and T₃. Dotted lines mark the point of interception of the regression lines T₁ and T₂, with T_ip=7.7 cm and A^1/2 _ip=76.3 km

Fig. 9.

Current velocity vectors in the South China Sea at a the surface (derived from June mean ship drift data; Levitus 1982) and b 900 m water depth (re-gridded from data modeled for the southwest-monsoon period by Chao et al. 1996). Scales of velocity vectors are 0.2 and 0.004 m/s. Pinatubo tephra thickness contour intervals (in mm) are as in Fig. 1