Monday, August 22, 2016

Detailed Alluvial Mapping with July Aerials in Western Washington

Reviewing aerial images is a routine part of my work. Over time the images have become better and better with images over the past decade being of substantially greater resolution and detail compared to older images. And of course color images are more typical today than the black and white images up through the 1990s. 

The set images below were taken in July 2015 and are of an area in western Washington. The timing of the images captures the window of time as grass pastures begin to dry out and grass goes dormant. The variability of drying out tells a story of the underlying soil.  

Alluvial fan from creek coning out of a steep forest slope to the southeast
Old channels underlain by gravel have turned brown sooner than the areas underlain by silt
The interpretation was confirmed with test pits dug on the fan surface

Another fan, there may be some mowing and animal paths as well 

Old river flow paths are obvious in the tree filled abandoned channels but are also evident in the soil. 

Sunday, August 21, 2016

Drought and a Lawn Weed Notes

This summer has proven to be dry and of late very warm relative to average records. I have had a lot away time from my home, but this has been a dry year for my small garden plot. Good ripening for the tomatoes but they are not as robust as they should be due to my neglect.  
Our other new home base where Lisa has her studio is a new landscape and ecosystem so I do not have a memory of what is normal. So my observations have no context for comparison.
Big leaf maples began dropping leaves a couple of weeks ago

Vine maples are not turning color just drying up

The two maple species have few leaves left

The trail back into the forest has a very fall look although the temperature was in the low 80s

The lawn is dormant but a few green weeds take advantage of the dormant grass

Those "weeds" are habitat
Numerous butterflies and honey bees enjoy the weeds
I missed a photo chance at a favorite - anise swallowtail
The above is an unknown skipper

The rabbits like the same lawn weed

If I have learned anything about this new ecosystem it is that a lawn weed is much appreciated by my new neighbors.

Thursday, August 18, 2016

Naselle River Notes

I was digging through some historic sources on the Naselle River area in southwest Washington and spotted this classic tree-like drainage pattern within a farm field.

2013 (USGS)

The field is protected from salt water inundation by a dike along the river bank which presents tidal water from flooding the fields. But this is a wet area and with low elevation and very shallow groundwater the filed id covered with drainage patterns consistent with a tidal marsh.

This particular field has not changes much over the aerial photographic period>

1953 (USGS)

These lands were settled fairly early by American settlers. Fishing, oysters, calms and timber with ready access to water for transport attracted early resource extractors. First nations peoples (Chinooks) had already used these bays and inlets for oyster gathering and trade. The farming soon followed with dikes and flood gates converting the rich alluvial estuary soils to pasture.

Investigations by Brian Atwater starting in the 1980s identified drowned forests along tidal areas of Willapa Bay and in the tidal areas of the Naselle River. These areas had been higher in elevation and then subsided during a large Cascadia subduction zone earthquake. The trees were killed by the flooding of the forest with salt water. Tsunami related sediments are present along many of these tidal areas. Post earthquake, alluvial sediment from floods has also covered these low lying areas with a layer of silt and mud.  Excellent soil if one can keep the saltwater out. 

Wednesday, August 17, 2016

Bjornstad: Lake Sacajawea Flood Bar

Bruce Bjornstad has been putting together a series of videos on ice age flood features. The latest is on a huge gravel bar on the lower Snake River. The ice-age flood features on the lower Snake are some of the best evidence of the scale of the massive floods. It is not possible to assign these features to other actions.  

Sunday, August 14, 2016

Eagle Geology and a Drain Pipe Perch

On many shoreline bluff visits I observe bald eagles. We are fortunate in Washington that they have become such a common site. As common as they may be they are still fun to observe.  I spotted this eagle while walking a shoreline bluff along the Strait of Juan de Fuca and observing the steep bluff geology above me. He was in a classic perch - a wind sculpted tall mature Douglas fir near the edge of a steep high bluff.
Perfect viewing spot atop a fir.

A bit after passing by the eagle perch, I watched the eagle soar out over the water. The bird headed back with no catch, but seemed to be taking a close look at the same features I was looking at - the bluff geology.

Eagle and outwash geology of sand and gravel with rip up blocks of silt

Eagle and glacial drift 

Eagle and more drift

The eagle did not return to its tree perch, but instead alighted on a drain pipe protruding from the bluff face.
 The way the bird headed on its flight strongly suggested this was a well known perch versus a sudden interest in geology by bald eagles.

The eagle was high enough above me to not be too concerned with my presence. The bluff here is about 100 feet high. At times like this I sometimes wish I had a better camera with me. But given the rough field work I do I am fairly happy with my small point and shoot Fuji. I leave it to better equipped folks to get the really good wildlife shots.

Saturday, August 13, 2016

Fire and Madrones

I paid a revisit to a burned over slope in western Washington. This is a slope that has a southwest aspect, is well within the rain shadow of the Olympic Range, and much of the slope is underlain by sand and gravel. Hence, a dry place that has remained a small prairie (small-prairie-at-discovery-bay).  During a previous winter visit I had noted that madrones were growing from burned stumps. In the two years since the growth has continued. Fire clears out the competing trees and the madrone is well suited for this setting.   

This prairie has been long lived. A sketch image from the Vancouver exploration of this area shows a grass slope at the same location in 1792. I suspect that First Nations use of the area enhanced the frequency of fire.

It is nice the see that madrone (Arbutus menziesii) is thriving here much as it did in 1792 when Archibald Menzies described the tree in detail while visiting the bay. Hard to image he did not walk up this prairie slope examining and collecting plants while visiting in May 1792.

Tuesday, August 9, 2016

Bald Mountain from Lake Cavanaugh

I've posted about Bald Mountain before (see bald-mountain). This is just a different view. This time from the south side of Lake Cavanaugh.

Bald Mountain is a block of greenstone within the Helena-Haystack Melange. The melange is a mixed slice of ocean floor that was thrust onto the edge of North America. It is one of numerous tectonic terrains in Washington State. Makes the bedrock geology of northwest Washington interesting as rocks of wildly different histories and ages are juxtaposed. The bedrock under the south shore of Lake Cavanaugh is much younger and is of local derivation, but just up the hill behind where I took this picture is yet another completely separate terrain of rocks with yet another different history.