Soils and Slope Relationships in Astoria – A Concern by Art Limbird

I have great reservations about the apparent need/desire to develop certain parts of Astoria for residential and even commercial use on sloping land poorly suited to such development.

I call attention to city land to the west of 3rd off Niagara and Madison on the ‘south slope’ – land that currently is forested. To me, there are good reasons why this land has not been developed and is forested. The unstable slope conditions are vulnerable to the weight of buildings and roads and it appears that landslips have occurred in the area in the past. Looking at the west side of this same area, there are truncated streets such as Alameda, Denver and Clatsop that help to substantiate the instability. Selling this land for residential development may prove to be a costly mistake.

In fact, there is evidence that many parts of Astoria are affected by naturally unstable slopes, made more hazardous by so-called development. Cutting into the base of slopes, adding weight to slopes with homes, other buildings, roads, etc., and ‘lubricating’ these slopes via watered lawns and disturbed drainage patterns compound the mechanisms of slope failure.

Since I have lived in the area – about 9 years – there have been several examples of slope movement and instability:

• near Safeway [about 31st and franklin] where the slope base was compromised for intended stores – now ‘shored-up’ by large rock rip-rap

• homes upslope from Astoria high school on Waldorf Circle which slid and cracked open – apparently affected by ‘activities’ at the slope base behind the school

• on-going subtle slumping on niagara ave. Just east of 15th around the corner from the ‘slide area’ sign

• significant landslide on bond street that has diverted water and sewer lines, etc.  [check back to 1953-54 to see the major landslides in this same area!!]

Note: I was interviewed by a Portland TV reporter just after the bond street slide but the interview did not appear on TV. I believe my comment that ‘much of Astoria is vulnerable to landslides’ was too much to handle in a short news clip!

• most recent slide on Duane Street west of 8th that is threatening several downslope houses and has created a very steep slope

• several abandoned and un-inhabitable homes around the ‘rim’ of the north and west sides of Astoria hills due to land movements nearby

In addition, there are many locations throughout Astoria where there are steep concave-shaped slopes = back slope of a ‘fault’ or ‘slump block’ and land slip and the downslope ‘debris pile’ of slumped material. In fact, much of Astoria was built on the slump material from the 1700 earthquake and tsunami.  This material now is described as ‘colluvium’ in the Clatsop County soil survey report.  Colluvium is “the material [also called talus] which accumulates at the base of a slope”. Most of Astoria sits on ‘rotted’ mudstone that is loosened and ready to move even on gentle slopes.

The article in the Daily Astorian of October 18, 2013 “landslide maps signal alert for Astoria” seems to be ignored in the interest of selling off lands. However, a ‘pairing’ of site observations and soil mapping can determine which slopes are more vulnerable and which slopes are safer.  The combination of soil landscape [topography], plus slope aspect, plus soil ‘parent material’ will provide the answer – safe or sorry development location.

Note: my qualifications are: soil geographer with 30+ years of research and field experience in soil characteristics and formation. I have worked with soil properties, soil erosion, soils related to land movements, and buried soils. I have worked in Ohio, Alberta, St. Vincent, and Jamaica on soil/land use reports and projects. Now I am working with the North Coast Land Conservancy and the willapa bay national wildlife reserve with soil related projects.

Respectfully submitted,

Dr. Arthur Limbird
Associate Professor Emeritus
University of Calgary