Whatcom County Council is in the early stages of struggling with the concept of lahar hazard. Lahar hazard has been a challenging issue for all counties and cities potentially impacted by lahars coming off Washington State's glacial clad volcanoes. Lahars are large landslides that travel down into valleys below volcanoes. Lahars can be generated during eruptions, but they can take place without any volcanic activity.
The lahar paths to the northwest of Mount Baker will impact Whatcom County. The flow paths to the south will also reach Skagit County.
For comparison, the map below shows the lahar risk areas associated with Nevado del Ruiz, a glacier clad volcano in Columbia. A lahar from this volcano killed thousands at Armero located approximately 30 kilometers from the summit of the volcano.
Lahars have come off of Mount Baker in the past. A lahar deposit is exposed along the banks of the Nooksack River east of Deming.
Lahar deposit near confluence of North Fork and Middle Fork Nooksack River
(Photo Kevin Scott, see http://pubs.usgs.gov/fs/2000/fs059-00/)
The Baker lahar is similar to the thickness of the lahar that was fatal from Nevado del Ruiz.
The Nevado Del Ruiz lahar was associated with a small eruptive event. Well within the types of small eruptive events that will take place on volcanoes in the Cascade Range including Mount Baker.
Understanding lahars also means understanding what lahars can do to people and communities.
This video provides a good over view of the impacts to people from a lahar (caution - it is graphic):
It needs to be emphasized that large lahars or landslides off of volcanoes do not require an eruption. The images below are from a lahar slide off of Mount Meager, an old volcano in British Columbia that can be considered the northern edge of the volcanic Cascade Range (Guthrie and others, 2012).
Image credit: Mika McKinnon