#bettergeology

[bettergeology]

See that white layer in this hillside? That's an extremely important white layer. 680,000 years ago (give or take), a large volcanic system in what is now Wyoming erupted catastrophically, spewing ash and debris across the North American continent. You might have heard of it, it's called Yellowstone Caldera. You may notice that these pictures in no way resemble the verdant forests of the Rocky Mountains and that is because they are from Death Valley, California, located more than 620 miles (1000 km) away from the Yellowstone Caldera!

But... it gets cooler.

The hills this ash layer is exposed in, the Kit Fox Hills, have been uplifted. The mudstone and sediments here are ancient valley fill, meaning that they used to be the bottom of the valley and are now about 400'/120 m above the current valley floor. This is the action of the Northern Death Valley fault zone, one of California's longest active faults. In this area, that fault has some excellent outcrops as seen below.

Next door to Death Valley to the west is Panamint Valley. It's not quite as big or dramatic as Death Valley but it has many of the same sorts of geologic features which have formed over a shorter geologic timeframe, interestingly. The faults in Panamint Valley just move faster than those in Death Valley so things are a little more youthful over there. In the middle of Panamint Valley, we see this same Yellowstone ash layer but with a caveat - instead of a mere 400 feet, in Panamint Valley that ash is more than 500 feet above the valley floor! That suggests that the valley subsidence of Panamint Valley is about 20% faster than Death Valley. The true story is more complex than that, but it's good as a reference point. Let's see what that looks like.

It's hard to see in this aerial imagery, but near the top of this steep escarpment is that same volcanic ash layer. It's a bit thicker here because this big pile of material I've outlined is an ancient delta. Panamint and Death Valleys have repeatedly hosted large lakes during cooler and wetter times. This huge delta deposit is over 1.2 million years old at the base, and about 600,000 years old at the top (above the Yellowstone ash). As the Panamint Mountains (background) rose and the valley subsided, huge amounts of eroded rock and gravel were dumped on this delta. So what you're looking at is a 1 million year-long record of the floor of Panamint Valley! How cool is that?

[samdaniyar2020]

Thrust system, flower structures and transpressive duplexes in Zeidun-Kareim Belt, Central Tectonic Province, Egyptian Nubian Shield (East African Orogen)

[bettergeology]

Taking a stroll in the ephemeral brines of Death Valley.

As a basin completely isolated from the sea, Death Valley is the ultimate sink and final destination for all of the surface and groundwater for an immense area of eastern California and central Nevada. Following an unusually wet summer and winter of 2023/2024, a lake as deep as 3 feet filled the salt pan on the flood of Death Valley and brought back a glimpse of how it must have looked when the valley contained a permanent lake in the geologic past.

Strong winds during my last visit actually pushed the lake some two miles to the north, churning up the sediment and mud of the lake bottom and turning the water to the color and consistency of chocolate milk. As the salty water evaporates from the surrounding mud, it draws the salt into long, threadlike crystals that turn the salt flats fuzzy for a brief time.

[bettergeology]

As seems to happen fairly regularly, I found myself in the John Day Fossil Beds again, leading and helping out with geology hikes through the hills.

The particular topics I wanted people to get out of this hike was the relationship between rock strength and landscape shape. See the round, symmetric hill in the center of the above photo? It is made of almost unconsolidated (soft) clay and silt with very low strength. Below it is a cliff ledge of much harder rock, an ancient lahar (volcanic mudflow) which turned to concrete-like stone after flowing down an ancient river valley. This harder rock sits directly below the soft clay, holding it up.

Even in places where rocks and hills all look roughly the same, as in this part of Oregon, there is often incredible nuance to be found within the landscape.

[bettergeology]

The cobble beach at Yaquina Head Area of Outstanding Natural Beauty, Oregon.

Cobble beaches are uncommon - they are a regular beach but instead of sand they are made of… well, cobbles. They require a source of hard rock, powerful waves to keep the sand from piling up, and enough time to tumble the hard rock into rounded cobbles. Yaquina Head has all three of these things! Sticking out about a half mile into the Pacific Ocean, Yaquina Head is a rocky finger of basalt about 16 million years old. It's one of the most distant outcrops of Columbia River Basalt, which flowed all the way from huge fissures in the Washington-Oregon-Idaho border area about 300 miles (500 km) to the east! At that time, this was underwater and the basalt was flowing into underwater canyons and infiltrating the soft ocean mud. This caused all sorts of strange formations within Yaquina Head, and also explains why the rock is so fractured (called brecciate in geology terms) with so much orange glassy sand in the outcrops. The powerful waves wash the orange oxidized sand (called palagonite) away, leaving behind solid hunks of basalt which slowly tumble and round out over hundreds of years.

The Pacific Ocean crashes headlong into this beach, beating the basalt with relentless power, just as it has done for over 16 million years.

[bettergeology]

(Lava) Bomb on the Mountain (volcano)

South Sister is Oregon's 3rd tallest peak. It's a stratovolcano 10,363 ft (3,158 m) tall, part of the Three Sisters complex which includes dozens of smaller volcanoes and several older eroded mountains.

The upper 2,000 feet or so (~650 m) is a 20,000 year-old cinder cone, the result of a fire-fountain-type eruption of lava. One of the common features of that style of eruption are lava bombs - chunks of liquid lava flung through the air that cool in streamlined and elongated shapes. The upper flank of the mountain is very steep, and makes for slow climbing through cinders. Slope pitches average 30˚ in this area, and get as high as 58˚!

Perched at random on this slope is probably the largest lava bomb I've ever seen! It's probably about a meter across and shows the streamlined, elongated nature of a bomb very well. I'm not sure why it's still sitting at that precarious location, but up close you can see the vesicular texture of erupted lava (basaltic andesite). This might be classified (yes, there are sub-classifications of lava bombs - geologists love classifications!) as a breadcrust bomb because it looks almost like a crusty bread with cracked crust. These are very common on volcanoes like this. It's hard to see in this picture, but amidst the vesicles (bubbles) in the rock are numerous plagioclase feldspar crystals ~0.5-1 mm across.

Anyway, volcanoes are cool.

[bettergeology]

Basalt columns in basalt of Newberry Volcano, lower Crooked River Gorge, central Oregon. Each one is 60-120 cm across (2-4 feet).

[bettergeology]

Ticked an item off the “visit” list a couple weeks ago: Little Crater Lake, in the Mount Hood National Forest.

It’s sort of an oddity- a near-circular straight-sloped clear blue lake in the middle of a large wetland. It seems to sit right on top of a bedrock fault, which is likely active, part of a series of extensional faults called the Oak Grove Graben (which was completely unknown until about 2020!). The thinking is that this fault allows copious amounts of groundwater to rapidly rise with enough force that it washed out this crater-shaped lake. Its similarities with real Crater Lake end there, as that lake is an enormous volcanic caldera. Nevertheless, it shares the same vertigo-inducing clarity which allows the natural deep blue of very cold water to be so striking.

We found a healthy rough-skinned newt population in the lake. I guess the cold doesn’t bother them that much! Lots of flowers were in bloom, including this lovely Western Bunchberry.

[bettergeology]

Debris-flow breccia, Mosaic Canyon, Seath Valley National Park, California, USA.

[bettergeology]

Mosaic Canyon at dusk, Death Valley National Park, CA.

August 2024.

Flickr

[bettergeology]

You’ve probably heard of the “sailing stones” in Death Valley, where the rocks apparently move across the lakebed and leave tracks behind them in the mud. Find out what makes that happen in my new video!

[bettergeology]

Much of western Washington's recent geology has been dominated by giant ice sheets stretching from the Canadian Rockies to central Washington. This ice gouged out the Salish Sea, Puget Sound, and carved up the rest of the landscape. Port Townsend sits on a peninsula made up of the junk giant glaciers left behind. This is typically sandstone, gravel, and mud but weird stuff starts happening when the giant glacier meets the ocean and starts to melt. There's lots of cool geology in Port Townsend, once you know where to look!

[bettergeology]

Ubehebe Crater

At the north end of Death Valley sits a small volcanic field. About 2,100 years ago, a body of basaltic magma forced its way to the surface along the Tin Mountain Fault, reaching the surface near the floor of Death Valley.

2,100 years ago, Death Valley was a different place. It more closely resembled the rest of the Mojave Desert's scrubby vegetation, and cooler temperatures allowed for more water to be present across the region. A shallow lake permanently occupied what is now called Badwater Basin, and other marshy regions were found along the length of Death Valley. As the body of basaltic magma rose to the surface, it encountered the significant groundwater deposits present. When lava meets water, explosive things happen.

(looking SW along the Tin Mtn. Fault)

A phreatomagmatic eruption occurs when magma encounters water and creates a near-continuous steam explosion. Ubehebe Craters consists of about 15 explosion craters, called maars. These many craters probably all formed about the same time, with the main Ubehebe Crater being the last one formed and therefore not filled with volcanic ejecta and debris. As the steam-magma slurry rose, it blasted through the surrounding rock which is a conglomerate composed of solidified alluvial fans coming off the surrounding mountains. Of the material erupted and thrown across the landscape, only about 1/3 of it is lava! The dark blanket surrounding the volcanic field consists mostly of fragments of this conglomerate baked and altered by its proximity to lava. You can find basaltic cinders with chunks of conglomerate trapped within, often baked orange or white by the heat.

The main Ubehebe Crater is quite large, about 800 m wide (1/2 a mile) and 270 m deep (800 feet). There's a steep and slippery path to the bottom, from which you can get a true appreciation of the size and power available in the inside of a volcano. The surrounding layers of alluvial conglomerate are faulted and cooked, showing that this area has seen some intense geologic activity in its lifetime.

Brown and gray layers show the surge deposits left by individual explosions during the eruptive period which probably lasted between a few days and several weeks. They sit directly atop the preexisting arroyo/bajada/alluvial fan surfaces.

[bettergeology]

Colorful Clays of the Painted Hills area

The Painted Hills are one of the most popular and well-known of Oregon's scenic treasures. The towering ridges of yellow, red, and black clays reveal part of the complex geologic story of Oregon when the area was a tropical rainforest, or a hardwood temperate forest, or a volcanic hellscape at different times. The different bands and layers are folded, warped, and faulted by complex plate tectonics. Here though, at Painted Cove just behind the main Painted Hills viewpoint, the story is just a little different.

Painted Cove is a couple of shallow gullies linked in a loop by a boardwalk and trail. In here, you pass through areas of bold red and yellow clays before reaching a gully flanked with a light purple rock. The light purple is of a completely different origin than the clays, which are effectively fossilized soil layers.

This is a weathered outcrop of rhyolite lava, a lava composition that is mostly quartz by mass. This area grades from purple to brown to red. This is an actual preserved soil horizon. If you dig a hole, you go through different soil horizons - or chemical and physical conditions - before you reach bedrock. Commonly these are O (for organic-rich), A, B, and C. B and C are closest to bedrock and include chunks of weathered, eroded source rock. Here, the purple is that C horizon, then the brown layer is B, and the red is an A horizon mantling the rhyolite lava flow. This whole stack of soil is somewhere around 25 million years old!

This is one of my favorite rock outcrops in all of Oregon because of how elegantly and simply it displays soil development processes from more than 25 million years ago!

(A note for other geologists: my soil horizon analogy isn't completely accurate since these paleosols have different classifications than regular young soils do, and I'm not very well-versed in those at all)

If you're in to photography, these are (with the exception of the 2nd to last shot) shot on Fuji Color 400 with my Nikon FM2.

[bettergeology]

What’s this? A new video from BetterGeology? Wow! Best to take a pause and see what’s going on with this recently-discovered fault in eastern Oregon.

[bettergeology]

Keeping an eye out

Mount St. Helens is the most active volcano in the Cascades. It's major eruption in 1980 has been succeeded by about 10 other smaller eruptions and maintains near-constant microseismicity. The first pictures show one of the close-in monitoring stations at Windy Ridge. The USGS Cascade Volcano Observatory maintains a number of large monitoring stations close to the mountain, near the vent, where they've been armored to protect from eruptive activity. These stations typically include a seismometer (seismogram here), a GPS station (the white dome), and other equipment like geophones or a webcam. Volcanoes never erupt spontaneously, they are always preceded by some kind of activity - usually small earthquakes - and let you know when they're ready to go. St. Helens hasn't done anything since about 2010, taking a well-deserved rest after the major lava dome growth in 2004-2008.

Around the mountain to the southeast, you can hike through the Plains of Abraham's pumice fields and past the slot-canyon head of Ape Canyon to the rim of the Muddy River, where another monitoring station reports seismicity and GPS data. The GPS stations observe the shape of the volcano over time. As gas, fluids, and magma move around inside the mountain, the surface deforms. Rapid or dramatic deformation is often indicative of impending eruption or other activity, and is one of the most important parameters in the volcanologists' arsenal.