Google Earth view of the iceberg marks, North Dakota
A couple of days ago John Freeland at the AGU page agu.org/terracentral/ noted iceberg marks on the former bottom of Lake Agassiz in North Dakota. It is one of those features that is essentially impossible to see from the ground but under the right conditions can be readily seen from say 20,000 feet as in the image above. Lorna Linch provides a short write up and illustration of her research on iceberg marks geog.qmul.ac.uk/staff/linchl.
The Google Earth view is noteworthy in that the default view emphasises the berg marks. Using other dates in Google Earth the marks are nearly or entirely invisible. The image above is a compilation mosaic with images from different times put together to emphasize pertinent features. The features stand out depending on moisture and possible wind blown snow. Difference in salt concentrations in the soils also plays a role in visibility.
I took a quick amateur look for iceberg marks on the floor of the former Sumas Lake that straddles the border between Washington and Canada in northwest Washington. I saw one possible feature, but I am highly skeptical and believe it is probably an alluvial feature. I suspect there has been far too much sedimentation to preserve any iceberg marks if they ever were present in the first place. I am not aware of any iceberg gouge marks anywhere in Washington. One thing to consider about the berg marks at Lake Agassiz is that the site is incredibly flat and very little sediment has been added to the area since. Any glacial lakes in Washington or glacial tidal areas are not nearly as flat.