A model by USGS volcanologists provides a ‘what if’ scenario for a Mount Baker ash eruption for any given day, based on actual reported wind directions and velocities at various altitudes from throughout the region. The computer model is updated each time a new wind report is issued, usually several times a day. These reports are entered into the computer model automatically. The results of each model’s runs are available to the public via the MBVRC website (links below). The model provides an animation of the spread of the ash cloud, and a thickness (isopach) map for the resulting ash accumulation beneath the plume.

Airborne ash plume (animation):

https://vsc-ash.wr.usgs.gov/public/public_results.php?ash3d_job_id=759&air_or_deposit_ind=A

Deposit thickness map (isopachs):

https://vsc-ash.wr.usgs.gov/public/public_results.php?ash3d_job_id=759&air_or_deposit_ind=D

(See notes on time, below.)

The model is based on field data for the 6600-year-old ‘BA’ eruption. This is the largest Mount Baker eruption preserved in the geologic record since the last glacial maximum. Although we don’t know the height of the eruption plume, or how long the eruption lasted, we do have well-preserved ash deposits. The thickness has been measured in many places in the northwestern Cascades (figure at left). A mathematical model* allowed an approximation of the erupted volume of BA tephra: 0.2 cubic km. For comparison, on May 18, 1980 Mount St. Helens erupted 1 cubic km (0.26 cu mi, or 1.4 billion cu yards, uncompacted).

The computerized model was written by Larry Mastin, Michael Randall, Hans Schwaiter, and Roger Denlinger. The paper describing the model is on-line at User’s Guide and Reference to Ash3d. The parameters for the eruption simulations shown were entered by Dave Tucker (MBVRC).

Note on TIME in these runs: Time in the models is given in UTC (Coordinated Universal Time). This is synonymous with GMT. The Pacific Northwest is 8 hours earlier (Standard Time), 7 h earlier during Daylight Saving Time. An ‘eruption start time’ of 2013-11-05 16:02:00 UTC means 8:02:00 AM PST, or 9:02:00 AM PDT.

The ash plume covers a lot more area than the ash deposit map. Deposit thickness will decline to insignificance closer to Mount Baker than the ash plume. The deposit from the distal ash cloud would be barely measurable at great distances from Mount Baker. But small proportions of tiny ash particles suspended in the plume may cause jet aircraft engines to flame out. The ash plume model depicts the plume over 24 hours.

A lot of data is available once you access the Run Results page, including Google Earth kmz files. Click ‘download data’ to access these files. Among other things:

If you select ‘deposit thickness inches’ (or mm, your choice) you will open a Google Earth overlay. The colors represent areas where ash from this eruption model would accumulate. Click on any square to see the thickness of accumulated ash.

Open ‘ash arrival times’ to see the impact on various airports (red squares).

Open ‘deposit arrival time’ to see the approximate time when the ash would arrive in a given area. You will need to look at the Ash 3D Run Results to determine what time the eruption started (remember, this is given in UTC). ‘Eruption start time’ is whenever new wind data arrives to be used by the model.

The model visualizes a scenario for an andesite eruption at Mount Baker based on the geologic record. Eruptions could be much smaller, or larger.

Significance of ash concentrations in the plume

The plume animation shows two colored zones, red inside blue. According to Larry Mastin (CVO), “the 0.2 mg/m3 concentration (blue zone) is roughly the detection limit of volcanic ash for modern (2-channel infrared) satellites. The 2 mg/m3 concentration (red zone) is what the airlines tentatively consider the threshold for engine damage. In Europe in 2010 during the Eyjafjallajökull eruption, they were using that as the boundary of the no-fly zone.”

The following is taken from The hazard of volcanic ash to aviation VAACs (Volcanic Ash Advisory Centres): New ash threshold value by Dr. Fred Prata, Climate and Atmosphere Department, NILU, Kjeller, Norway. http://earth.eo.esa.int/workshops/Volcano/files/4_PrataTalk1.pdf “The mass loading in the umbrella region of the column typically varies approximately linearly with the height of the volcanic ash column, from around 2500 mg/m3 for a column reaching 7 km to over 20,000 mg/m3 for one reaching 40 km. It has been estimated that the volcanic ash concentration encountered by the KLM 74 (ed. note: this aircraft suffered 4-engine failure, but restarted engines after a harrowing descent) during the Mount Redoubt (Alaska) eruption in December 1989 was of the order of 2000 mg/m3 . The response of a jet engine when exposed to volcanic ash depends on a number of variables, including the concentration of the ash, engine type, engine thrust setting, time of exposure and ash composition. The density of typical dry volcanic ash is given as 1.4 g/cm3 , and wet volcanic ash as 2 g/cm3. * BA tephra volume calculated using the method of Fierstein and Nathenson: Fierstein, J., Nathenson, M, 1992, Another look at the calculation of fallout tephra volumes: Bulletin of Volcanology, v. 54: 156 – 167.