![](media/image1.png){width="1.7479166666666666in"
height="0.6423611111111112in"}**Mount St. Helens Eruption Facts**

**Third Anniversary of the Current Eruption**

**September 20, 2007**

**[The Ongoing Lava-Dome Eruption]{.underline}**

-   **Lava dome growth slows**---Lava-dome building eruption of Mount
    St. Helens continues, but at a slower rate than in previous years.
    Over the past year, the rate of lava extrusion declined from 0.6
    cubic yards per second in December 2006 to 0.4 cubic yards per
    second in April 2007. This volume of extrusion is equivalent to
    emplacement of a small pickup-truck load every three seconds.
    Putting this growth rate in perspective, the rate has declined from
    7.8 cubic yards per second for a short time during the early months
    of the eruption in 2004. However, the current extrusion rate is
    equivalent to the average growth rate of Mount St. Helens over the
    last 4,000 years. At the current rate of eruption (0.35 cubic yards
    per second), it will take a couple hundred years for the volcano to
    rebuild itself to its former volume. Approximately 7% or more of the
    volume of the pre-1980 volcanic cone has been replaced;
    approximately 11% of the present horseshoe-shaped crater has been
    refilled.

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-   **Reduction in earthquake activity**---Earthquake activity has
    decreased significantly during the past year, but continues above
    pre-September 23, 2004 levels. At this time last year, rising magma
    produced hundreds of earthquakes daily. Presently, tens of
    earthquakes are noted daily. The seismic signals are dominated by
    signatures from rock fall and glacier motion.

-   **Lava dome growth continues, but no more whalebacks and
    spines**---Lava dome shapes have changed continuously since the
    onset of eruptive activity in October 2004. Early on we observed
    development of lava whalebacks (recumbent spines), which gave way in
    2005 to the growth of sharp vertical spines, which alternately rose
    and then crumbled as rock fall. During 2007, the extrusion has
    evolved from the development of sharp spines to a less dramatic
    broad area of growth beneath the location of spine 7.

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-   **Rock chemistry consistent with previous findings---**Throughout
    the current eruption, lava composition has been remarkably constant.
    Rocks erupted between 2004 and the present have a slightly higher
    silica content than 1980-1986 rocks (65 weight % versus 62 -64
    weight %), but they have distinctly different trace-element
    compositions and come from a shallower level of the magma reservoir
    beneath the volcano.

-   **No change in eruptive style in the foreseeable future**---The low
    volcanic gas fluxes, constant rock chemistry, and low seismicity,
    deformation and extrusion rates all suggest little to no change in
    eruptive style in the foreseeable future. The risks posed by the
    current eruption are relatively low. However, eruptions are
    inherently unstable situations and the USGS and the University of
    Washington's Pacific Northwest Seismic Network continue to monitor
    the situation closely.

**[Dome dimensions as of April 20, 2007]{.underline}**

-   **Lava dome exceeds volume of 1980-86 dome**---Maps from aerial
    photographs taken on April 20, 2007, indicate that the volume of
    lava dome erupted since October 2004 is 121 million cubic yards, an
    amount sufficient to fill approximately 163 Rose Garden Arenas
    (Portland, Oregon). Dimensions of the dome are 1,740 feet north to
    south, and 3,480 feet east to west. The high point is 7,569 feet
    above sea level. The April 20, 2007, lava dome area was almost 0.2
    square miles. Volume of the new dome exceeds that of the 1980-86
    lava dome (97 million cubic yards).

-   **High point of dome 200 feet below Shoestring Notch**---The high
    point of the present lava dome is 1,290 feet above the 1986 crater
    floor. This is slightly higher than the height of the Empire State
    Building in New York (1,250 feet), and shorter than the Sears Tower
    in Chicago (1,454 feet). The 7,569 foot summit elevation is slightly
    lower than the 7,772 foot dome that grew during the summer of 2006.
    Vertical distance between the top of the lava dome (7,569 feet) and
    the Shoestring Notch (7,780 feet and lowest point on the crater rim)
    is 211 feet.

**[Crater Glacier]{.underline}**

-   **Arms of east and west side glaciers approach convergence---**At
    present, the growing lava dome is squeezing the glacier against the
    crater walls, causing ice to thicken and flow more quickly out of
    the crater. The two arms are moving generally northward, but
    obliquely towards one another, and their termini, in early September
    2007, are approximately 180 feet apart. On April 20, 2007, the
    termini were approximately 400 feet apart. Between then and now, the
    glacier termini have advanced towards one another at a rate of
    approximately 0.7 feet per day.

-   **Glacier thickness**---Glacier thickness in the upper section of
    the east arm exceeds 500 feet. Ice thickness at the terminus of each
    arm is approximately 60 to 130 feet.

-   **Scientists remove seismic station Yellow Rock threatened by
    glacier**---In September 1981, University of Washington's PNSN
    scientists installed a seismic station within the crater that was
    dubbed Yellow Rock. At that time, no one could have foreseen that
    the station would survive the next five years of dome-growth
    activity, or that 26 years later it would be threatened not from
    rock but from ice. In early September 2007, USGS-CVO scientists
    dismantled Yellow Rock because of the threat of glacier ice, now
    just 100 feet away, from overrunning it or from a large boulder
    melting out of the ice, tumbling down and smashing it. In September
    2006, the glacier was 400 feet from Yellow Rock, but rapid movement
    of the glacier terminus over the past year made it seem unlikely
    that it would survive another year. In 2006 seismic station "Vault"
    was established in the crater at a greater distance from the glacier
    to augment the network.

-   **Crater Glacier exceeds area of established nearby
    glaciers---**Area of Crater Glacier is approximately one-fifth the
    area of glaciated terrain that existed on Mount St. Helens prior to
    the catastrophic eruption of May 18, 1980. Crater Glacier is
    approximately 0.33 square miles in area, which is more than twice
    the area of White River Glacier on the south side of Oregon's Mount
    Hood. Crater Glacier is the newest glacier to form in North America.
    It is one of the most rapidly advancing and one of the lowest
    glaciers in the lower 48 states.

**[Science Nuggets]{.underline}**

Volcanic eruptions provide unique scientific opportunities. Recent work
produced these science nuggets.

-   **Cameras provide close-up views of lava-dome growth**---During
    October 2004, scientists installed a time-lapse camera at Sugar Bowl
    on the northeast side of the crater mouth for the purpose of
    monitoring eruptive activity. This camera and one installed in 2005
    on the summit rim have collected thousands of images that document
    the evolution of lava extrusions, first as whalebacks, then as
    spines and now as more general rise over a broad region. During 2006
    and 2007 scientists installed additional cameras to support detailed
    analysis of dome movement. They are analyzing correlations between
    extrusion rates, tilt events and earthquakes.

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-   **Aeromagnetic Survey**---USGS scientists conducted an aeromagnetic
    survey to determine the distribution of hydrothermally altered rock
    and perched water. This work is similar to surveys completed at
    other Cascade volcanoes.

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-   **Electromagnetic experiments provide greater understanding of
    hydrothermal fluids beneath the crater floor**---USGS scientists
    conducted three weeks of electromagnetic experiments to learn about
    the circulation of hydrothermal fluids beneath the lava dome and
    crater floor.

-   **Comparisons of Mount St. Helens and Bezymianny volcano,
    Russia---** The USGS is participating in a 5-year NSF-funded
    Partnership in Research and Education (PIRE) project on volcano
    monitoring science and education in collaboration with the National
    Science Foundation, the University of Alaska, and the Institute of
    Volcanology and Seismology (IVS) of the Russian Academy of Science.
    The project\'s theme is a comparison of eruptive activity and
    volcanic unrest at Bezymianny volcano, Kamchatka, and Mount St.
    Helens, Washington---both of which underwent massive landslides
    (sector collapses) and related blasts and large eruptions (1956 at
    Bezymianny, 1980 at Mount St. Helens). On August 27- September 1,
    2007 the USGS Cascades Volcano Observatory hosted a workshop for 15
    Russian and American participants, including two members of the
    Russian Academy of Sciences, graduate students from the US and
    Russia, and scientists from IVS and CVO.

-   **Plate Boundary Observatory (PBO) ---**Borehole geophysical
    observatories: Mount St. Helens is now surrounded by four 800-foot
    instrumented boreholes, each about 5 miles from the crater. A
    strainmeter cemented into the bottom of each borehole can monitor
    expansion and contraction of the earth\'s crust around the volcano
    at the part-per-billion level. Just above each strainmeter is a
    3-component seismometer, to take advantage of the quiet recording
    conditions. The very sensitive instruments in these deep boreholes
    are designed to detect subsurface movements miles beneath the
    volcano. The borehole observatories are funded by the National
    Science Foundation as part of the Plate Boundary Observatory
    component of the Earthscope program, and were constructed by UNAVCO,
    Inc., a nonprofit consortium of geoscience research institutions.
    Data are available to the public at:
    <http://pboweb.unavco.org/?pageid=89>.

-   **New publication about Mount St. Helens will become available in
    2008**---The USGS has documented a broad range of knowledge about
    the ongoing eruption in a new publication that is now in final
    editing stages. USGS expects to publish this document in early 2008.

**. . .**