An ASHTAM is a special form of Notam, it should not be mistaken for a notam that merely mentions volcanic ash.
Defintion of ASHTAM
ICAO define an ASHTAM as
A special series NOTAM notifying by means of a
specific format change in activity of a volcano, a volcanic
eruption and/or volcanic ash cloud that is of significance to
Content of an ASHTAM
An ASHTAM should include the following items.
- Date And Time
- Volcano Name and Number
- Volcano Latitude and Longitude
- Volcano Level of Alert Colour Code
- Existence and Horizontal / Veritcal Extent of the Volcanic Ash Cloud [usually from the local VAAC]
- Direction of Movement of the Ash Cloud
- Air Routes or Portions of them and Flight Levels Affected
- Closure of Airspace and Air Routes and Alternatives if available
- The Source of the Information
- Any Plain Language Remarks
ASHTAM are valid for a maximum of 24 hours but can be issued as often as is necessary when there is a change in the nature of the volcanic ash cloud.
Further details can be found in the following documents
Which in turn reference these documents.