![](media/image1.png){width="1.7479166666666666in"
height="0.6423611111111112in"}**The Second Anniversary of the 2004 to
present eruption of Mount St. Helens**

**Bullets for Media Briefing, September 29, 2006**

Overview of the eruption

Volumes, dimensions and eruption rates

Current conditions

Significance the Mount St. Helens eruption

Some recent investigations

Other Work - New Alert Level Notification System

[Overview]{.underline}

-   Following 18 years of eruptive quiescence, Mount St. Helens began
    showing signs of unrest in late September 2004 and began a sustained
    dome-building eruption on 11 October 2004. The volcano continues to
    erupt today.

-   A series of steam-and-ash explosions began on 1 October through 6
    October, followed by the first appearance of hot rock above the
    glacial surface on 11 October 2004

-   Since dome growth began, there have been only two explosive events:
    one in mid-January 2005 and the other early March 2005. Neither
    event was preceded by precursory activity. Both destroyed numerous
    instruments within the crater, emplaced small pebbles on the crater
    rim and resulted in a light dusting of ash on the volcano's flanks.

-   Dome growth has been continuous since 11 October 2004. Six of the
    seven spines to date were extruded during the first year (October
    2004-October 2005).

-   The first of four prominent spines or whalebacks (smooth-sided,
    elongate extrusions of mostly solid rock) grew southward and to the
    east, impinging on and greatly deforming the east crater glacier.
    With the formation of spine 6 at the end of year 1, we saw a
    redirection in dome growth towards the west and the beginning
    deformation of the west crater glacier.

-   Activity over the past year (October 2005-September 2006) has been
    steadily ongoing but with a slower extrusion rate compared to the
    past year.

-   There have been no explosive events over the past year.

-   Since October 2005, lava dome growth has centered on spine 7. It's
    growth has been accompanied by numerous rockfalls The largest
    rockfall occurred on 29 May 06 that produced an ash plume that rose
    to at least 16,000 feet and a rock avalanche that swept over the
    eastern part of the 1980-86 lava dome, damaging two instruments and
    flowing about ½ the distance towards the crater mouth. This is the
    first time that a rock avalanche from a collapse has flowed beyond
    the margins of the 1980-86 lava dome.

[Volumes, Dimensions and Eruption Rates]{.underline}

-   By the end of year one (late September 05) the lava dome volume was
    about 67 million cubic meters (87 million cubic yards) growing at an
    average rate of about 2.3 m^3^/second (about 3 cubic yards/sec)

-   In February of last year, the lava dome was about 77 million cubic
    meters (100 million cubic yards), equaling the size of the 1980-86
    lava dome.

-   In mid-August 06 the volume was about 85 million cubic meters (111
    million cubic yards) growing at an average rate of less than
    1m^3^/second (1.3 cubic yards/second), which would fill about 150
    Rose Garden Arenas (Portland, Oregon)

-   Dimensions of the lava dome (mid-August 06) are: length, 3,314 feet
    (1010 m); width, 1,678 feet (510 m) and height above the 1986 crater
    floor 1300 feet (396 m)

-   At 1300' tall, the lava dome is higher than the Empire State
    Building in New York (1250'), but still shorter than the Sears Tower
    in Chicago (1454').

-   Worldwide lava dome eruptions occur over months (Redoubt Volcano,
    Alaska - Jan to April 1990), years (Unzen Volcano, Japan -- 1991
    to 1995) and decades (Santiaguito Volcano, Guatemala -- 1922 to
    present).

[Current Conditions]{.underline}

-   Over the past year, seismicity and volcanic gas fluxes have been
    low, deformation and extrusion rates have slowed, and there is no
    change in rock chemistry, which suggests little to no change in
    eruptive style; however eruptions are inherently unstable situations
    and the USGS and the University of Washington's Pacific Northwest
    Seismography Network continue to monitor the situation closely.

-   The lack of explosive activity coupled with continuing low number of
    earthquakes and small quantities of volcanic gas indicate that the
    risks posed by the hazards are relatively low.

-   The lack of explosive events over the past year, coupled with the
    westward migration of activity allowed scientists to walk on the new
    lava dome under relatively safe conditions

-   On 21 July, the US Forest Service reopened the climbing trail to the
    summit of Mount St. Helens allowing the public to get a bird's eye
    view of the activity within the crater. Before the Forest Service
    made their decision, the USGS and USFS had several discussions
    regarding the risks posed by the ongoing eruption and the types of
    events that climbers might experience at the rim.

[Significance of the Mount St. Helens eruption]{.underline}

-   This eruption of Mount St. Helens highlights the phenomenon of
    lava-dome building as a common and important contributor to the
    construction of volcanic cones worldwide. Mount St. Helens is just
    one of many volcanoes in recent decades to experience dome-building
    eruptions. Most of the major volcanic cones in the Cascade Range
    have been built in part by the eruption of lava as domes.

-   The ongoing eruption of Mount St. Helens offers an extraordinary
    opportunity to conduct close-up studies of volcanic activity. Easy
    accessibility permits scientists to conduct long-term and
    simultaneous measurements of seismicity, deformation and gas
    release, and close-up observations of the dome's growth habits.
    These data sets are among the most comprehensive and in-depth
    records of lava dome growth in the world. The ability to synthesize
    these data sets holds potential for providing new insights about the
    nature of lava dome growth worldwide.

[Some Recent Investigations]{.underline}

-   Scientists working on the "old part" of the new lava dome found
    evidence to suggest that the lava dome was essentially solidified
    within several hundred yards beneath the crater floor. The outer 5
    to 10 feet of the lava dome is composed of ground rock that
    transitions to solid rock with numerous fractures. These findings
    support the stick-slip model of lava dome extrusion. If the model is
    correct, it may help explain the origin of many of the million plus
    small, shallow earthquakes that have occurred during the eruption.
    These earthquakes may be the result of numerous sub-surface slips
    that created the ground and fractured rock. Scientists have also
    noted that for short periods of time (hours to perhaps a day) part
    of the growing lava dome appears to stick (no movement detected in
    photographs) and then restarts again after high-M2 to low-M3
    earthquake occurs, observations which again support a stick-slip
    model.

-   CVO scientists continue to be fascinated by the effect of the
    eruption on the glacier. Prior to eruption, we were concerned that
    renewed volcanism might melt a good portion of the glacier or create
    a glacial lake within the ice mass that would be catastrophically
    released, or that dome collapse or explosive events would melt the
    glacier and crater snowpack and send a lahar downvalley. To date
    none of these catastrophic scenarios have unfolded and instead we've
    watched the remarkable deformation of the crater glacier. Joe Walder
    will discuss what we've learned about the interaction of the growing
    lava dome with the glacier.

-   One of the challenges of the past year is determining whether the
    volcano is still erupting. The number of earthquakes has diminished
    greatly, Spine 7 has been too steep to place a GPS spider, and
    software problems have delayed the production of the digital
    elevation models. Jon Major will discuss how we've been deploying
    cameras in the field to get confirmation of continuing dome growth
    and other information about the eruption.

[Other work]{.underline}

-   The relatively low level of eruptive activity over the past year has
    allowed us to become more of a Cascades Volcano Observatory instead
    of just a Mount St. Helens Observatory, although Mount St. Helens
    remains the main focus. Most of the scientific staff have been busy
    this past winter writing up their data on the eruption for a special
    Mount St. Helens volume, hopefully to published in 2007.

-   In the past year, we have installed additional instrumentation at
    Mount Rainier, Mount Hood and Three Sisters; resumed debris-flow
    studies at the debris flow flume on the H.J. Andrews Experimental
    Forest; helped our sister volcano observatory, the Alaska Volcano
    Observatory, responded to this past year's Augustine eruption. And
    we have finally implemented (or soon) a new volcano
    alert-notification system for all U.S. observatories.

    -   [New Alert Notification System]{.underline}

        -   On October 1, 2006, the U.S. Geological Survey's Cascades
            Volcano Observatory (USGS-CVO) will implement a new volcano
            alert-notification system. The change is part of a larger
            effort by the USGS to adopt a common system nationwide for
            characterizing the level of unrest and eruptive activity at
            volcanoes.

        -   Under the new system, the USGS will rank the level of
            activity at a U.S. volcano using the terms *Normal*, for
            typical volcanic activity in a non-eruptive phase;
            *Advisory*, for elevated unrest; *Watch*, for escalating
            unrest or a minor eruption underway that poses limited
            hazards; and, *Warning*, if a highly hazardous eruption is
            underway or imminent. These levels reflect conditions at a
            volcano and the expected or ongoing hazardous volcanic
            phenomena. As part of the alert-level system, aviation color
            codes (*Green, Yellow, Orange, and Red*) are used to provide
            succinct information about volcanic-ash hazards to the
            aviation sector.

        -   For more information see the Volcano Hazards Program
            webpage: http://volcanoes.wr.usgs.gov