Our family took a vacation to Olympia National Park on the Olympic Peninsula of Washington state. We were very lucky to get good weather. Most days were sunny and the temperatures ranged from lows in the upper 40s to highs in the upper 60s to lower 70s. A welcomed relief from the Texas heat!

As always, we included stops to geologically interesting points. One such location was the shoreline of Salt Creek Recreation Area on the Strait of Juan de Fuca, a wave cut platform. The sea erodes the cliff face until a platform is created at sea level. The rocks present at the site are tilted layers of sandstone. A variety of organisms then take advantage of the habitat provided by the platform.

Wave-cut platform
Tilted sandstone beds
 The organisms we found on the platform included varieties of rock weed, muscles, barnacles, and sea anemone to name a few. These organisms live within the intertidal zone. That is the zone between mean low tide and mean high tide. In order to preserve moisture and avoid drying out, the animals will often close up into a shell or leathery membrane to wait for the tide to return.

Gooseneck Barnacles are present in the center of this photo. Above them are the more typical recognised acorn barnacles. Near the bottom left portion of the photo are some mussels.

Larger green sea anemone and smaller aggregating anemone are present in a tide pool along with mussels and rock weed.
Because the rocky shoreline does not deliver much sediment to the sea and the water is so deep seaward of the platform, the water is crystal clear. The water is so clear that this site is one of the best shore diving sites in the US. There is a kelp forest in that deep water that makes the water appear to be rather thick. Many fish and invertebrates live in these kelp forests. Sea otters (although we did not see any), cormorants, and sea gulls are some of the air-breathing animals that make use of the kelp forests for food and protection.

Kelp forest off shore of the wave-cut platform.

As we were preparing to leave Salt Creek Recreation Area that evening, the fog rolled in as it commonly does along the coast of Washington.

Foggy ending to a lovely visit.

 In addition to visiting the coast along the Strait of Juan de Fuca on the northern part of the peninsula, we also visited the Pacific Coast. Rialto Beach is within Olympia National Park. In order to visit the tide pools and be able to walk the 1.5 miles to the "Hole in the Wall," we had to arrive at the beach a or just before low tide. Low tide the day we visited was at around 10 am. Morning fog is common along the coast so, we had a very foggy and misty walk along the beach. Rialto Beach is about 20 miles west of Forks, WA which receives approximately 114 inches of rain each year. Forks is approximately 30 miles west of the Hoh Rainforest which receives approximately 200 inches of rain annually. Therefore, it was not surprising that we got wet!

Hiking out to the Hole in the Wall 1.5 miles north of Rialto Beach. It was raining lightly at this time.

The rocks that makes up the sea stacks and the exposed rock along the coast are composed of a variety of marine sandstones which were deposited in the deep sea before movement of the plates uplifted the rocks and erosion exposed them at the surface.

Three sea stacks in the mist, Rialto Beach, WA
Sea stacks are created when the waves take advantage of cracks and fractures in the rock and preferentially weather those areas until the stack is separated from the main body of rock. Oftentimes, a sea arch is created first and then when the rock making up the arch collapses, a stack is created.

The Hole in the Wall, a sea arch, at Rialto Beach, WA.

The Hole in the Wall is a 1.5 mile hike from the parking area for Rialto Beach. The Hole can only be accessed during low tide. This sea arch is through weak layers in the sandstone. As the waves crash on the rock, they will continue to erode the rock, enlarging the hole until the arch collapses creating a new sea stack and a new cliff on the landward portion. This arch is inaccessible at high tide. Anyone caught on the other side of the arch when the tide advances far enough to cut off access, will have to wait until the next low tide to return to Rialto Beach. Therefore, when hiking along beaches with cliffs and headlands, it is imperative to know the tide schedule for that area. Getting caught by a rising tide cannot only leave one stranded, it can be deadly.

Just like at Salt Creek, the rocky tide pools team with life. Ochre sea stars in brown, orange, and purple; green sea anemone, aggregate anemone, mussels, barnacles, rock weed, encrusting algae, sea urchins, and many others can be found in the tide pools. Although I looked thoroughly, I never found a sea urchin.

Ochre sea stars. Purple, brown, and orange are common colors. These sea stars were so plentiful in places that I had to be careful where I placed my feet so as not to step on one. These are the top predator in the intertidal zone. They feed on mussels, barnacles, and other such creatures. The bottom photo is now on permanent display at the National Zoo in Washington, DC in their Pacific NW coast display.
Green sea anemone with pink encrusting algae surrounding it.
Although smaller than the green sea anemone, the aggregate sea anemone are just as beautiful.
Below I have included a video from the Science Learning Network that contains footage of the tide pools along the coast.

Working Between the Tides from Science Learning Network - NPS on Vimeo.

Although the creatures found on the beach were a highlight, the rocks were just as interesting. The sandstones and mudstones that make up this rocky shoreline were once at the bottom of the ocean. As the Juan de Fuca Plate collided with the North American Plate, the Juan de Fuca plate was forced under (subducted) the North American Plate. As often happens, some of the rocks and sediments deposited on the descending Juan de Fuca Plate were scraped off and stuck onto the overriding North American Plate. In the process of being scraped off and uplifted, the rocks were tilted, folded, and faulted. The series of photos below illustrates the effect of these processes.

Tilted layers of sandstone and mudstone.
Folded and faulted layers of interbedded sandstone and mudstone (lens cap for scale).
Glaciers played a huge roll in the developement of the landscape that we see on the Olympic Peninsula. The rivers that meet the Pacific Ocean once drained the melt water of the large continental ice sheets to the ocean. As a result, these rivers carried large quatities of sediment. The deposits of glacial till (sediment deposited as a result of the action of glaciers) contained many different kinds of rocks that were plucked from many different locations. These rocks were then transported by the rivers to the ocean where they were reworked along the coast. As such, a wide variety of cobbles are present on the beach: basalt, gabbro, diorite, granodiorite, granite, sandstone, chert as jasper, andesite, to name a few. It makes for an interesting scavenger hunt along the beach!

Beach cobbles. Nearly white ones with black specs: granodiorite, Dark gray ones: basalt or sandstone, Red ones: chert as jasper, Yellow and tan ones: quartz.
Fun with pebbles and cobbles!

The Olympic Mountains are part of the Coastal Range which runs along the west coasts of California, Oregon, and Washington. These mountains are the direct result of the tectonic activity occurring nearby. The rocks within the Olympic Mountains were once on the bottom of the ocean. The sandstones and mudstones that make up the mountain were deposited in the trench created by the subduction of the Juan de Fuca Plate beneath the North American plate. These rocks contain fossils which were on the ocean floor 15-20 million years ago. That means that the Olympic mountains have been standing for less than 15 million years!

Glaciers have affected these mountains since their very beginning. Because the Olympic Mountains are along the west coast of North America, they catch the very moist westerly winds blowing off the Pacific. As the moist air is forced to rise up the mountains, the colder temperatures at altitude force the clouds that form to drop their moisture, often in the form of snow. The snow fields are deeper in the Olympic Mountains than they are in the Rocky Mountains. Therefore, the Olympic Mountains are more glaciated than the Rockies.

Glaciers on the Olympic Mountains
Olympic Mountains

Folded quartzites (formerly sandstone) and slate (formerly shale) on Hurricane Ridge. A close up of this outcrop is presented below. Note the quarter for scale on the lower photograph.

The Hoh River originates in the Olympic Mountains. Much of the water this river carries is glacial meltwater. Note the gravel bar in the middle of the river.
Fast moving water in the Hoh River
Tim playing with the cobbles along the shore of the Hoh River.
The gravel in the Hoh River, found along the shore, in bars, and on the river bed, were delivered to the river during the last ice age. Today, the river just shifts the cobbles as it moves them slowly downstream. There is too much sediment in the river for the river to handle as a result the river collects the gravel in bars and shifts those bars continuously throughout the year. As a result, most of the bars are not vegetated.


The finale of our trip was a drive up to the Johnston Ridge Observatory to see Mt. St. Helens. Prior to May 18, 1980, Mt. St. Helens was a beautiful, conical-shaped, composite or stratovolcano. One of five volcanoes in the Cascade Range of Washington. The others include Mt. Baker, Glacier Peak, Mt. Rainier, and Mt. Adams. At 8:32 am on May 18, 1980 after a landslide caused by an earthquake released the pressure on the volcano, Mt. St. Helens exploded. For nine hours it belched a column of ash 30,000 feet into the atmosphere. Although considered small by volcano standards, Mt. St. Helens ejected approximately 0.1 cubic miles of material.

The eruption and lateral blast reduced Mt. St. Helens' elevation by 1300 ft. All living things within the blast zone were killed either by the exceedingly hot, fast moving blast material or by burial beneath it.

Fifty-seven people perished in the blast (see map below.) One of the victims was David Johnston. He was a young volcanologist working for the USGS through the Cascade Observatory in Vancouver, WA. He was sitting on a ridge approximately 6 miles from the volcano. The team felt confident that that location would be out of range of any pyroclastic flows and too high for any mudflows to reach them. Unfortunately they did not suspect that the volcano would first explode laterally destroying everything in it's path for nearly 12 miles. As Mt. St. Helens began erupting, David Johnston's last words heard over the radio were "Vancouver, Vancouver! This is it!" To honor him, the ridge and the observatory built there were named after him.
See interactive map here.

First glimpse of Mt. St. Helens on the drive up to the Johnston Observatory.
The North Fork of the Toutle River is a tiny ribbon in the upper portion of this photo running from left to right. This river is cutting through the lahar (mudflow of ash and water) deposits from the 1980 eruption. The floodplain of the river is poorly vegetated partly as a result of the major amounts of low nutrient ash deposited.
Getting closer! All the trees in this photo have regrown since 1980.

Mt. St. Helens as seen from the Johnston Observatory, approximately 5.5 miles from the volcano. No trees have regrown on the flanks of the volcano because the ash is very unstable and it has few nutrients available until it has weathered sufficiently to release necessary ions.
Close up of the mountain. The volcanic dome is visible within the crater. Eruption of sticky, rhyolitic lava will eventually rebuild the volcano back to its conical shape so that one day, it can erupt again. The surface of the volcano is cut deeply by drainage channels. These channels coalesce to form the North Fork of the Toutle River.
Pyroclastic flow and debris flow deposits at the base of the volcano are downcut by streams. These streams have downcut more than 30 feet. 

The lateral blast mowed down trees as it blew through. Large noble spruce trees were felled like blades of grass. Limbs, needles, and bark were stripped from the trees.
The right slope of this hill faces Mt. St. Helens. The trees were mowed down in the direction of the blast from right to left. The trees on the slope of the hill that did not face the volcano were left standing however, the heat burned off their needles, smaller limbs, and bark. Reforestation of this hill has been difficult as the soil was blown away or buried under volcanic material blown from the volcano.
The trees in this stream bank were in the lahar (volcanic mudflow) produced by the eruption of Mt. St. Helens.
Layers of different varieties of tuff. Lens cap for scale.
Ashfall tuff overlain by lava flows. Road cut is along the road leading to the Johnston Observatory.
A fault is present in this photo running from the upper left to the lower right middle portion of the photo. In this example, the hanging wall has moved down relative to the footwall. Therefore this fault is a normal fault.

A close up of the fault showing fault gouge within the fault zone. Fault gouge is created by the rocks on either side of the fault grinding against each other. This material is very friable and is easily weathered as a result. That is the reason why the fault is recessed into the rock face. Lens cap for scale.

While flying home we had the pleasure of seeing Mt. Rainier out of our window. Note the conical shape of this volcano. On this day, the cloud ceiling was quite low so the valleys are obscured. Fortunately Mt. Rainier rose above the clouds so we could see it perfectly!

This is a close up of Mt. Ranier. Note the bowl-shaped cirques near the top of the mountain, between ridges. Cirques are where glaciers begin. As the glacier grinds up and removes the rock beneath it, the ridges become higher and steeper until they are broken apart by weathering.

Upon close examination of this photo, the crevasses within the glaciers are easily seen. Crevasses are created when the ice cracks as it flows over the uneven rock beneath it.

Visiting the Olympic Peninsula was a feast for this geologist's eyes. Many beautiful geological processes, formations, and rocks were visible in a relatively small geographic area. I highly recommend visiting the often missed part of our country!

1 comment:

  1. That looks like so much fun! I have a 7 year old daughter and we all went camping at Big Sur, CA for our family trip last Spring Break it was amazing. We try to take a yearly family trip. I will have to try and send you pictures from that trip. It is definitely a beautiful place and a must see if you love the outdoors.
    Savannah Riley
    Geology 1403