A November Sighting of Vanessa atalanta on Orcas Island

Vanessa atalanta (red admiral) is one of the most widespread butterflies in the world. I do not spot them very often and my first inclination when this one caught my eye was it was a Limenitis lorquini lorquini (Lorquin's admiral), a butterfly I frequently see (lorquins-admiral). But in this case the markings were obviously wrong.   

This one was sunning itself on a south facing bedrock cliff of the Constitution Formation on Orcas Island. I was enjoying the sun and the south facing rock myself while waiting for a ferry to Lopez. I took care not to disturb the butterfly. Sun on a November day had not been expected nor was seeing a butterfly this late in the year.

The week before I noted a patch of young nettles on Orcas Island - the food source for Vanessa atalanta pupae. I was a bit surprised to see young nettles in the forest in the fall - more typically they are a early spring plant. Perhaps the mild San Juan winters provide a niche habitat for this butterfly. 

Visit to the Lopez Structural Complex at Richardson

The end of the road at Richardson on the southern shore of Lopez Island provides an easy to access view of part of the Lopez Structural Complex. 

Richardson is named for the original land patent holder. He was granted the land shortly after the San Juan Island was determined to be part of the United States after a couple of decades of dispute between Great Britain and the United States regarding claims to the islands. 

The community of Richardson grew as a commercial and fishing center in the late 1800s through the early 1900s. It was well positioned as a protected deep water port for transporting farm products off the island and bringing goods to the island. A cannery for the fishing industry was located at the bay shore to process salmon that were netted via net traps set along the south shore of the island. Over time agricultural changes, fishing changes and the location of the ferry on the north side of the island led to the commercial development fading away. For a time a store at the end of the road was a destination for visitors - I once ate a large ice cream cone after a bike ride to the south end of the island. The abandoned dock and bulk fuel facility remain, but the store is gone. 

Former bulk fuel storage tanks

Old dock with Olympic Range in the distance across the Strait of Juan de Fuca.

The road end at the old bulk fuel facility provides easy access to views of a portion of the Lopez Structural Complex (LSC). This location is discussed in Brandon (1989), Brown and others (2005) and Brown, Housen and Schermer (2007). Relative to other parts of the LSC this area appears somewhat coherent; however, this site has some highly deformed and fault bound units as well.

Just below the end of the road along the shore are great exposures of pillow basalt.

Pillow basalt. Note sheared zone at base of pillows in picture

This basalt is an ocean floor basalt. The pillow structures are hardly disturbed at all despite having been once deep within a subduction zone trench more than 20 kms below the surface.

A short distance away the pillows are deformed.

Stretched and deformed pillows

At the road cut above the shore a contact between greenish metamorphosed volcanic rocks and maroon mudstones is a good example of why the Lopez Structural Complex is called a complex.

Analysis of micro fossils in the mudstone suggest an age of 112-115 Ma (million years) (Brown and others, 2005). The mudstone and the contacts along the mudstone appear to be highly sheared.

Shearing within the LSC often appears to be more intense as tectonic stress and fault movement may preferentially take place within weaker rock units. Brown and others (2005) also dated metamorphic minerals in the pillow basalt and found metamorphism of the basalt took place at 124 Ma. Hence, the pillow basalt is older and was deep in the subduction trench when the mudstone was formed. The mudstone was not deposited on the basalt, but the two units were faulted so that they are now abutted with one another.

This finding has implications for trying to piece together the assemblage of accreted terranes that make up northwest Washington - a very tough puzzle that has led to very different interpretations.

The complexity of the LSC and the context of the LSC within the accreted terranes of northwest Washington and western North America is a lot to take in. Besides getting a little perspective of tectonic geology it is simply nice to see well exposed bedrock and structures in western Washington.

I liked this small exposure as it captures an observation Brandon made about trying to decipher tectonic deformation from soft sediment deformation.

Behind the mail box it is clear these rocks have undergone multiple deformation events.

Tight small fold adjacent to shear surface

Pillow basalt being made unrecognizable

Highly sheared volcanic breccia

Shore Bluffs, Sediment and Beaches: One Example

The composition of beach sediment is dictated by the source material for the beach as well as wave energy. A common beach type in western Washington is gravel and cobble beaches with scattered boulders.

East shore of Lopez Island

The sediment source is from an eroding bluff that extends to the south.

Glacial erratic boulder embedded in a poorly sorted glacial till

The sediment source for this beach is glacial till. The silt and clay content is much greater than the gravel, cobble and boulder content, but the fine grained silt and clay is readily transported off the beach by wave action.

Typically I would call this bluff a "feeder bluff". That is erosion of the bluff provides sediment to the beach, and hence, feeds the beach. MacLennan and others (2013) came up with a mapping scheme to identify and map feeder bluffs.

This particular bluff was mapped as a transport zone, not a feeder bluff. In this case the erosion rate is very slow due to the very moderate wave energy combined with the very hard resistant glacial till. The fact that much of the slope is vegetated and in many areas tree covered further suggests that this shore bluff is providing very little sediment input. Another possibility is that the toe of the slope did not exhibit the erosion shown above when the shore reach was mapped.

Another mapping scheme might be to call this a slow feeder bluff. For rapid erosion bluffs that send lots of sediment to the beach, MacLennan and others (2013) use the term "feeder bluff exceptional", but for slow erosion sites like that shown above they use transport zone. That is a reach where sediment is transported along the beach with very minimal input from the bluff.

Shore reach designations can be important in regards to shoreline regulations. Feeder bluffs in particular are important; if the sediment source from a feeder bluff is stopped, the beach will become starved and the beach will disappear - a loss for recreation and habitat. Hence, the effort to identify and map these shore forms.   

Rubus ursinus

There are various plants that present field work challenges in western Washington. Rubus ursinus or trailing blackberry is a low key plant that has temporarily flustered me while navigating through brush. 

Rubus ursinus set as a couple of trip wires on a moss covered log

High stepping and an awareness that a wire like vine may be wrapped around an ankle is a key strategy

The sharped barbs are not long, but they are very effective at shredding skin

The blackberry is a native and does produce tasty fruits. They are far less problematic compared to thick Himalayan blackberry thickets or rose thickets. 

Forest Blocking Debris Flows

Debris flows and debris floods area a significant hazard on alluvial fans.  Forested alluvial fans can significantly reduce the debris flow and flood hazards. A forest stand of stout trees can act as a stationary rake preventing large wood debris from spreading out on the fan surface. I have been to several alluvial fans where homes were saved by the presence of forest on either side of the stream on the fan, and I have seen homes destroyed that likely would not have been impacted if the forest had not been removed. 

The debris flow path shown above came off of a very steep mountain slope. The debris flow initiated as a small shallow slide about 1,500 feet in elevation above this point. The slide mixing with creek water flushed out the accumulation of large wood within the steep channel and delivered the pile of logs with mud and water to the base of the mountain.

Forest along the side of the stream kept the wood debris as well as the stream confined to the existing stream route.

From a land use geology hazard policy, leaving forest stands on some alluvial fans can be a form of mitigation, but also a restraint on property owners from cutting trees and thereby increasing the risk to neighboring properties. I have recommended leaving trees on several development projects. At least one county has utilized restrictive covenants on permits based on those recommendations. 

Ground Fog During the Dry Spell

Northwest Washington has had a nice stretch of sunny weather. The air has cooled quickly in the evening along the ground with frost in places. But overhead, even in the morning it has been warmer. I noted sharp swings in temperature on even modest rises in the land while heading out on my various ventures.

The mix of clear sky and ground fog made for nice scenery.

Heading towards the Chuckanuts across the Samish Flats

Cattle on Lopez Island

Baker to the left of large cottonwood/eagle tree and Twin Sisters to the right 

Fish and Wildlife land in the foreground

Lummi Peak 

Thick ground fog 

Another band of fog forming over field and spilling across road

Western Washington should turn back to cool and wet again. Nice scenery as well - just different.

Orcas Landing Feeder Bluff

I visit Orcas Landing on a regular basis as it is the location of the ferry landing for Orcas Island.

For shoreline wonks there is an example of an armored feeder bluff just to the east of the grocery store.

Feeder buffs are eroding shoreline bluffs that provide sediment (feed) to beaches. By lining the feeder bluff with a rockery armor at the top of the beach, erosion of the bluff is stopped. The result is a well vegetated bluff as well as a protected road at the top of the bluff. The unarmored bluff further to the east (right in the picture above) has eroded with the subsequent loss of vegetation. The downside of armoring feeder bluffs is that the beach becomes starved of sediment and non armored areas may see a substantial increase in erosion. The loss of sediment supply from erosion will also lead to the loss of the beach.