# Presentation: 252051

## Improving Ashfall Advisories

*the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of *
*Geological and Geophysical Surveys*

**Improving Ashfall Advisories**

## Current situation

- No simple operational tool or model to accurately forecast fallout area and amount (e.g. thickness) is used routinely in Alaska; existing models are either inadequate or difficult to run quickly
- Model development has focused on ash cloud motion
- Ashfall warnings (NWS and USGS and others) lack standardized language
- Augustine lesson: confusion about impacts and lack of guidance about areas of concern – including aircraft facilities on the ground

## In development

- User-friendly ash fallout graphical tool for AVO and possibly NWS use based on a New Zealand approach is under development
- Long-term goal is to develop a more robust model that uses more realistic inputs and approaches
- Standardized ashfall advisory terminology proposed for adoption
- Clearer public guidance statements
- Better coordination of messages among agencies

## Draft terms proposed by USGS and NWS

| TERM | Accumulation
(inches) | Key Impact Thresholds 
(cumulative)  | Core Call-to-Action Statements  |
| --- | --- | --- | --- |
| Trace or 
Dusting | <1/32 in | Eye and respiratory irritant, very low level impacts for most people. | Avoid excessive exposure to ash which is an eye and respiratory irritant. Those with respiratory sensitivities should take extra precautions to minimize exposure.   |
| Light | 1/32 – 1/4 in | Possible crop, animal equipment, and infrastructure problems; widespread clean-up likely. | Avoid excessive exposure to ash which is an eye and respiratory irritant.  Seal windows and doors.  Protect electronics and cover air intakes.  Minimize driving and listen to your local radio station or National Weather Service Radio for further information. |
| Moderate | 1/4 – 1 in | Ash removal efforts significant. | Avoid excessive exposure to ash which is an eye and respiratory irritant.  Seal windows and doors.  Protect electronics and cover air intakes.  Avoid driving and listen to your local radio station or National Weather Service Radio for further information. |
| Heavy | 1 – 4 in | Weaker roofs begin collapse at ~ 4 inches of wet ash accumulation. | Avoid excessive exposure to ash which is an eye and respiratory irritant.  Seal windows and doors.  Protect electronics and cover air intakes.  Remain indoors unless absolutely necessary.  Exercise extreme caution clearing rooftops.  Listen to your local radio station or National Weather Service Radio for further information. |
| Very Heavy | 4 in – 1 ft | Roof collapse, damage to trees, essential services interrupted. | Avoid excessive exposure to ash which is an eye and respiratory irritant.  Seal windows and doors.  Protect electronics and cover air intakes.  Remain indoors unless absolutely necessary.  Exercise extreme caution clearing rooftops.  Listen to your local radio station or National Weather Service Radio for further information. |
| Severe | >1 ft | Roads impassible, severe 
infrastructure damage, heavy plant and animal loss. | Avoid excessive exposure to ash which is an eye and respiratory irritant. Remain indoors unless absolutely necessary.  Exercise extreme caution clearing rooftops.  Listen to your local radio station or National 
Weather Service Radio for further information. |

**Draft terms proposed by USGS and NWS**

## ASHFALL WARNING MESSAGE

- WWAK72 PAFC 180001
- NPWALU
- URGENT - WEATHER MESSAGE
- NATIONAL WEATHER SERVICE ANCHORAGE AK
- 840 AM AST TUE JAN 17 2006
- AKZ161-180230-
- BRISTOL BAY-
- INCLUDING...KING SALMON...DILLINGHAM...NAKNEK...PILOT POINT
- 255 PM AST TUE JAN 17 2006
- ...**ASHFALL WARNING** IN EFFECT UNTIL 5 PM AST THIS AFTERNOON FOR THE
- ILIAMNA AREA...
- THE ALASKA VOLCANO OBSERVATORY HAS REPORTED THAT AUGUSTINE VOLCANO
- ERUPTED AROUND 758 AM AST THIS MORNING.
- AN ASH CLOUD HAS BEEN DETECTED BY THE NATIONAL WEATHER SERVICE DOPPLER RADAR AND WAS REPORTED BY PILOTS. A LIGHT AMOUNT OF ASH IS CURRENTLY FALLING AT ILIAMNA BUT AS MUCH AS 1⁄4 INCH COULD FALL BY LATE THIS AFTERNOON.
- AVOID EXCESSIVE EXPOSURE TO ASH WHICH IS AN EYE AND RESPIRATORY IRRITANT.  THOSE WITH RESPIRATORY SENSITIVITIES SHOULD TAKE EXTRA PERCAUTIONS TO MINIMIZE EXPOSURE.  SEAL WINDOWS AND DOORS. PROTECT ELECTRONICS AND COVER AIR INTAKES.  AVOID DRIVING AND LISTEN TO YOUR LOCAL RADIO STATION FOR FURTHER INFORMATION.
- FOR ADDITIONAL INFORMATION VISIT WWW.VOLCANO.GOV
- THE NEXT STATEMENT WILL BE ISSUED AS NECESSARY.

## Ash Fallout Forecasting

**No standard technique/method for estimating ash accumulation on the ground**
**Several models in use:**
**ASHFALL (Hurst and Turner, 1999)**
**Tephra 2 (Connor, et al., 2001; Bonadonna, et al., 2005)**
**Fall 3D (Costa et al., 2006)**
**HAZMAP (Macedonio, et al., 1988; Barberi, et al., 1990)**
**These are all advection-diffusion models based on Suzuki, et al., 1983**
**ASHFALL has received limited use for Alaskan eruptions (Augustine, 2006)**
**It did a poor job of reproducing known fallout patterns documented for the 1992 eruptions of Crater Peak**

## ASHFALL Model Simulation for Sept. 16-17, 1992 Crater Peak Eruption

- Comparison of the ASHFALL simulations with tephra thickness measurements of McGimsey, et al. (2001) for the Sept. 16-17, 1992 eruption of Crater Peak.
- The model underpredicts ash thickness for areas far from the vent (>250 km) and overpredicts thickness for areas closer to the vent (<250 km)
- This is largely due to the uncertainty in assigning values for the various input parameters which is somewhat arbitrary.
- This problem is compounded if the model is used as a forecasting tool where input parameters are unknown.
- Also, it is impossible to know beforehand what the particle size distribution of the ash cloud will be and thus it is difficult to estimate the settling velocity of the various particle size classes that make up the ash cloud.

## Ash Fallout Forecasting

**A more defensible approach to the problem is to combine distance - ash thickness relations for known eruption types with output from ash cloud tracking models such as PUFF**
**PUFF can define the approximate spatial extent over which fallout is likely**
**A simple power law relation based on known ash fallout provides an estimate of thickness at any distance downwind of the vent**

## Ash Fallout Forecasting

**Operational use of other advection-diffusion models is not yet practical because of the run times required**
**USGS will be developing new methods/techniques for estimation of ash fallout, but it may be several years before a realistic, user-friendly model is available... **