Photogeologic maps of the 2004-2005 Mount St. Helens eruption

The 2004-5 eruption of Mount St. Helens, still ongoing
as of this writing (September 2006), has comprised chiefly
lava dome extrusion that produced a series of solid, faultgouge-mantled dacite spines. Vertical aerial photographs
taken every 2 to 4 weeks, visual observations, and oblique
photographs taken from aircraft and nearby observation
points provide the basis for two types of photogeologic
maps of the dome--photo-based maps and rectified maps.
Eight map pairs, covering the period from October 1, 2004,
through December 15, 2005, document the development
of seven spines: an initial small, fin-shaped vertical spine;
a north-south elongate wall of dacite; two large and elongate recumbent spines (“whalebacks”); a tall and elongate
inclined spine; a smaller bulbous spine; and an initially
endogenous spine extruded between remnants of preceding spines. All spines rose from the same general vent area
near the southern margin of the 1980s lava dome. Maps
also depict translation and rotation of active and abandoned
spines, progressive deformation affecting Crater Glacier,
and distribution of ash on the crater floor from phreatic and
phreatomagmatic explosions. The maps help track key geologic and geographic features in the rapidly changing crater
and help date dome, gouge, and ash samples that are no
longer readily correlated to their original context because of
deformation in a dynamic environment where spines extrude,
deform, slough, and are overrun by newly erupted material.