Obsidian Gone Wrong

Near West Thumb Geyser Basin are a couple of short trails that had been calling my name since I arrived in Yellowstone 6 weeks ago. Very scenic, one leads to a small lake and the other climbs 500 feet to a ridgeline overlooking a fair portion of western Wyoming.


The trail down to Duck Lake is only ½ mile long. Since this is bear country, I was armed to the teeth with bear spray, my park radio, and a loud voice. “Hey bear! Get out of there!” I would sing incessantly as we marched through the spruce and lodgepole pine forest, new growth since the massive fires of 1988 that burned 793,880 acres, fully a third of the park.

Duck Lake


Trail to Duck Lake

A variety of ducks were bobbling about on the lake – Barrow’s goldeneye and bufflehead (or maybe they were scaup) – but they were too far away for any good picture and positive identification. They also refused to cooperate by coming closer.

As we headed back up the trail I noticed some familiar rocks lying about on the trail – pumice! That frothy, gas bubble–rich volcanic rock that I had spent so much time lobbing into Naknek Lake at Katmai last summer appeared like an old friend. Hey! I know you!

Yellowstone pumice

After our blistering one–mile hike we needed to re–fuel so we wandered over to the picnic area at The Basin.  I could have sat there all day and listened to the wind in the trees, but we had new trails to hike and views to absorb.


Yellow violet


Lake Overlook trail

We watched and wondered what treats the cowbirds and Clark’s nutcrackers were feeding on so intently in the meadow. Elk poop, perhaps? Pine seeds?

BrownHeaded Cowbird_Clarks Nutcracker
Cowbird and Clark’s nutcracker


Clark’s nutcracker

The trail climbed 500 feet in that one easy mile to a ridge overlooking Yellowstone Lake and the Absaroka Mountains to the east. Southward we could see the Red Mountains with Mt. Sheridan’s snow-clad peak. Beyond, the jagged Grand Tetons were adrift in the cloudy horizon.

Yellowstone LakeFrom Overlook Trail
View east towards Lake Yellowstone and Absaroka Mtns.


(L)Red Mountains and Mt. Sheridan; (R)Tetons in distance

I got on my elbows and knees to photograph some glassy volcanic rock along the ridge, but when I got home the images were a fuzzy mess. ACK!!! Obsidian gone wrong! I must go back!

Hot spring with grasses and yellow monkeyflower


Hot spring with grasses and yellow monkeyflower


Mountain bluebird


Glacier lily

I’m back and I’m blogging! It’s been a whirlwind week since I’ve been able to post anything. As an interpretive ranger here at Yellowstone I am required to prepare and present seven different original programs on various topics, and believe me, that prep time really takes a serious chunk out of any leisure opportunities.

Although most of my spare time has been taken up with reading about and composing programs on the resource that is Yellowstone, I had a major breakthrough yesterday. I devoted an entire day off to pounding out the grand-daddy of them all, my evening program – and I finished! Ninety-four PowerPoint images later, I have what I consider a nicely put-together, 45-minute evening program on – what else? – the geology of Yellowstone. I gave it the enticing title “Sleeping Giant.”

I have had some down time and found a few good chances to hike, however. Last Friday, hiking-buddy-Sasha-who has-the-same-day-off-as-me and I drove over to the Old Faithful area with the intention of getting to Mallard Lake. Our goal was to do the 3.1–mile trail which gradually climbs one of the resurgent domes of the ginormous subterranean magma chamber lurking beneath the park.

Examining Mushrooms

As Sasha mused over mushrooms, I took notice of the boulders and what looked to me like bubbles of glassy obsidian. There were obsidian gravels everywhere, eroding like crystals from a granite (although I knew this wasn’t the case), and some of the obsidian was mahogany. Exciting! My geologic map of Yellowstone describes these volcanic rocks as simply “Quaternary Central Plateau Rhyolites” without going into more detail about specific flow names or dates.
Obsidian Gravel
ObsidianBoulder (2)

ChipmunkOn ObsidianBoulder

Mahogany Obsidian

At around 2.5 miles we got turned back by too much snow and decided a cool beer at Old Faithful Inn would be a lovely ending to our afternoon of barely strenuous trekking. So we said our thanks and goodbyes to the chipmunks, marmots, and obsidian of Mallard Lake Trail and toodled our way back down the path.

YellowBellied Marmmot
StreamGravelsOf Mahogany ObsidianI went to Jackson yesterday, and I messed around. For some reason I don’t think old June and Johnny were singing about Jackson, Wyoming, but that’s just a minor detail. I needed to run some errands. I had a theme song. All was right in Nina-land.

First and foremost I needed to find a couple of stuffed beavers for my Junior Ranger program on beaver adaptations. I admire the little critters and their industriousness, but they are not easy to find, neither on the shelf nor in the rivers and streams.

So on my way south from Grant Village I stopped at the Colter Bay visitor center in Teton National Park and elbowed my way through a gaggle of unruly children who were sitting on the floor near the stuffed animals. “Hey! I’m the adult here! Get out of my way before I step on somebody! I need a beaver!” A path cleared in no time. I cuddled my two new beaver best friends all the way to the cash register and out to my car.

Then it was on to Jackson and some more messing around.

I checked in with MY TRAVEL AGENT from the parking lot of the Jackson Hole Visitor Center. I was face-to-face with a fierce-looking sculpture of a grizzly surprising some elk and I needed reassurance and a friendly voice. I soon found another friendly voice at the information desk. Those people were really nice! I got a pile of maps and had no trouble choreographing myself about the strange town. My favorite map was the huge paper placemat-type with all the streets and businesses drawn in. I love those!

I found the whole foods market where I spent too much on organic veggies and apricot/mango newtons. I am also a sucker for the bulk nuts and granola items. The clerk offered me the “Thursday 10% Senior Discount.” ME??? Wait a minute! When did this “senior discount” thing start happening?

Next it was on to lunch (an overpriced, tepid burrito) and the supermarket where I walked up and down every single aisle and spent even more cash. Everyone was so darn polite as our carts kept crashing into one another, squeezing along in the narrow aisles with shelves of canned green beans, pasta sauces, and bakery items. Apples and avocados were rolling off the produce displays left and right and out of the door but I had to keep focused.

I was able to lighten the load of the K-Mark small appliance department by one toaster oven before my 3PM haircut appointment. The stylist had been recommended by one of my interpretive ranger co-workers who lives in Jackson, and although the cost was a bit pricey by my standard (my standard being $4 at a local beauty school), I was really happy to finally have someone cut my hair who knew what she was doing. It was the best cut I’ve had in years and definitely worth the cash.

My last stop was the liquor store for some adult beverages. The sommelier recommended a sangria from Spain. I must have looked at him like he had two heads because he said “I know what you’re thinking but it’s really good.” So I bought a box. I am truly a sucker for a sommelier’s suggestions.

Then it was time to head for home and my little nest at Grant Village, Yellowstone National Park. Distance is only about 80 miles one way from Jackson but time-wise it takes two hours, so four hours of my day had been spent driving. The mountain scenery was spectacular, even in the drizzly fog of the day. When I finished unpacking my car I was exhausted. But since I had my two new best friends to cuddle and keep me company, I was fine. For the rest of the evening we sang June and Johnny songs and had a big old time.


Barely escaping hypothermia and an almost certain demise during my spur-of-the-moment venture into the frigid high country of Dunraven Pass and the Washburn Range last week, I soon forged onward in my endeavors. Actually, I did not so much forge onward as I simply forged back down the mountain. By this time the gray clouds had thinned to patchy blue sky but the temperature hovered around 38°F. I cruised down that twisting mountain road with a song in my heart – I was bound for Norris Geyser Basin, my original destination for the afternoon.

Norris is located outside the boundary of the latest 640,000–year–old Yellowstone caldera (the circular basin formed during the collapse of the volcanic crater) but inside the boundary of the oldest (and largest) caldera created around 2.1 million years ago.

Image courtesy of USGS

The map image above describes the three main caldera boundaries, with Island Park, at around 1.3 million years old the second and smallest, found in eastern Idaho. It shows that the youngest (most recent) volcanic explosion overlapped a fair part of the oldest one and so would have obliterated much of the evidence for this oldest explosion except mainly in the southwestern part of the park and eastern Idaho.

Most of the other hydrothermal features we see today in the park are within the youngest Yellowstone caldera boundary. Many hot springs and fumaroles (steam vents) in Norris reach temperatures above the boiling point of 200°F. Since Norris is also one of the hottest, most acidic, and most dynamic of the park’s thermal areas, I have been curious about the connection between this distinction and its location.

As part of one of the world’s largest active volcanic systems, it also sits on the intersection of three major faults. Two faults intersect with a “ring fracture” formed during the 640,000–year–old caldera collapse. It is these conditions which helped to create this dynamic geyser basin.

Norris Geyser Basin

Norris has the greatest water chemistry array among all of Yellowstone’s hydrothermal areas. As the water levels fluctuate in the underground hot water reservoirs beneath the geyser basin, concentrations of chloride, sulfate, iron, and arsenic also change. Norris’s thermal waters also contain the highest concentration of silica, which is the primary component of glass and many quartz beach sands.

I cannot help but wander around in sheer amazement at these geyser basins. The rainbow colors, bubbling mud, hissing steam, and overpowering odors of Porcelain Basin contrast starkly with Back Basin and its thermal features scattered and isolated amidst spindly and stunted lodgepole pines.

Porcelain Basin


IMG_6984Back Basin
Back Basin

Many of the colors seen in Norris Geyser Basin are evidence of heat-loving organisms called thermophiles.

Orange coloration is often a result of the presence of iron and arsenic in the thermal waters.

In general, yellow deposits contain sulfur; some of the thermophiles form communities in the hottest acidic thermal runoff at temperatures between 140°F and 181°F.

Dark brown, rust, or red colors in runoff channels contain varying amounts of iron. These thermophilic communities often form in water below 140°F.

Algae are the dominant life form in the emerald–green mats coloring many runoff channels, forming in temperatures below 135°F.

Dark blackish–green mats form in even cooler waters.

IMG_6943Runoff FromPinwheel AndWhirligig
IMG_6939 Thermophiles 
IMG_6947Runoff FromPinwheel Geyser
Colors within thermal waters change, too, because temperatures and chemistry change. In hot springs, the hottest water is nearest the vent coming from deep underground. As the water flows on the ground away from the vent, the water gradually cools. The chemical composition of the thermal runoff waters also changes as water flows from some particular feature, mixes with other water sources, and is either diluted or concentrated. As temperatures or chemical composition change, the heat-loving thermophiles gravitate to a more favorable location in the runoff channel.

The “Norris Geyser Basin Trail Guide” published by the Yellowstone Association has been my invaluable reference and trail companion.

After five week days of work and two weekend days exploring the park, I am finally beginning to get my bearings around Yellowstone. I had serious plans for those two days off – I wanted to cram as much sightseeing into them as possible. Somehow, though, I was lucky enough to cram in a bit more than was originally planned.

Since Thursday I’ve driven in sleet across just-opened Dunraven Pass, walked through sulfurous steam all over Norris geyser basin, hiked in snowy mud from Artist Point to an overlook overlooking the lower falls on the Yellowstone River, gotten delayed in bison jams in Hayden Valley, taken tons of photos, and loved every minute of it. The weather has gone from sunny to cloudy to spitting snow sideways to drizzly sleet mixed with rain and back to sunny blue sky and everything in between. As of yesterday morning, much of West Thumb of Yellowstone Lake was still littered with broken ice but the rest of the lake is an ice-free frigid blue.

PumicePointOn WestThumb
I had not intended to drive across Dunraven Pass. My initial intent had just been to go to Norris from Grant Village. The highest road in the park, it connects Canyon Village with Tower Junction and goes across the pass at 8880 feet above sea level, (or 8859 feet, depending on which map you’re looking at). It is generally closed all winter due to heavy snow and more recently due to avalanches. But the road had opened the previous day, and I was right there at Canyon, so I thought to myself – why not? It’s my day off – I can do whatever I want!

So off I sailed up the mountain at the lightning speed of 35 mph. The winding road was clear but the snowdrifts on the sides of the road kept getting deeper and deeper. As the road crested Dunraven Pass, rain turned to hail; soon sleet was blowing sideways and I wondered if they’d close the road again while I was up there and no one would know where I was and I would freeze to death in my little Subaru with just a measly Clif bar to nourish me during my final days on Earth.

So I parked at the pull-out anyway, put on a jacket, and got out of my warm car. I figured I might as well take a look around at my final resting place. The interpretive sign read “Heart of the Caldera.” I took this as a good omen.

RoadsideSign DunravenPassDunraven Pass sits on the northern edge of the giant Yellowstone caldera. Standing up there, I was able to get a sense of the immense size of it even viewed through the sleet and heavy gray clouds. It measures roughly 45 miles northeast to southwest and 30 miles northwest to southeast. The center of it is mostly forested and flat terrain, covered by one lava flow after another after the last major monster eruption of ≈ 640,000 years ago that blew beyond forever some 240 square cubic miles of magmatic and crustal real estate. This latest mega–eruption overlaps and obscures an earlier, even bigger event (if you can imagine anything so ginormous occurring at all) located more to the southwest which exploded ≈ 2.1 million years ago, taking an estimated 600 square cubic miles of Earth’s geology with it.

WashburnHot SpringsAndCalderaRim

To the east is Washburn Hot Springs, steaming in the image above in the bare, gray areas surrounded by forest. The springs exist due to hot water rising along the fault lines which encircle the caldera floor.
So the road across the pass seems to traverse the side of Mt. Washburn, at 10,243 feet one of Yellowstone’s highest peaks and a popular day hike. As I gazed about, I wondered about summer hiking prospects on Washburn, and exactly when the snow would be melted so some visiting friends and I could attempt a July assault on the trail. I hadn’t thought to bring any snowshoes.

NorthSide DunravenPass
WashburnRangeIt’s been three weeks since I arrived at Yellowstone and I’ve been to the Upper Geyser Basin an average of once a week. There is definitely some kind of attraction going on between me and these geothermal features.

Firehole River, Upper Geyser Basin, Yellowstone NP

Old Faithful, in the Upper Geyser Basin along the Firehole River, seems to be the most famous geothermal feature in the park. It erupts more frequently than any of the other big geysers but it is not by any means the largest spouter, reaching an average height of a mere 140 feet. The tallest active geyser honor belongs to Steamboat Geyser in the Norris Geyser Basin. Totally unpredictable, Steamboat can experience days, months, or even years between major eruptions, but when it blows it can reach heights of more than 300 feet. The last known eruption of Steamboat occurred in 2005.   I’m hoping it will erupt the next time I’m standing next to it.

The first time I walked along the boardwalks of the Upper Geyser Basin and watched Old Faithful erupt was two days after I arrived in Yellowstone. I saw so many geysers, hot springs, pools, mudpots, and fumaroles that I could not help but be astounded and nearly speechless. These things are literally everywhere!

BoardwalkUpper GeyserBasin(a)
SouthScalloped SpringUpperGeyserBasin

A second time I was fortunate to watch Old Faithful erupt during training, and then last week I went back again with a co-worker (it’s only 19 miles from Grant Village) to amble along the trails and boardwalks out to Morning Glory Pool.

FireholeRiver SashaForScale

MorningGloryPool (a)
Morning Glory Pool
Grotto Geyser

So what exactly is a geyser, anyway?

Geysers are rare birds. They require a unique set of geological conditions in order for them to even exist at all. Taken alone, these conditions are nothing special, but the combination of them is what makes geysers so extraordinary. Geysers require a water supply, a plumbing system, a volcanic heat source, geyserite, and earthquakes. This post covers the water situation with a bit of plumbing thrown in.

According to the definition developed by the US Geological Survey, a geyser is a hot spring characterized by intermittent discharge of water ejected turbulently and accomplished by a vapor phase.
Geysers are hot springs. Some springs do erupt cold water, but these are not by-the-book geysers. Hot involves any water above 98.6°F, the average human body temperature.

Geysers erupt periodically or intermittently, not continuously. They spend some amount of time recovering from one eruption and preparing for the next.

Geyser eruptions are turbulent, not calm. There is no required minimum height for this turbulence. If the water surface is broken by the activity it is considered turbulent. A few inches of height qualifies.

Lastly, constrictions in the geyser’s underground “plumbing system” prevent water from freely circulating to the surface where heat could escape. Water that has fallen as rain or snow and slowly percolated downward over the centuries to more than a mile deep can reach temperatures upwards of 400°F – 500°F or even higher. Pressure surrounding this water also increases with depth. The increased pressure exerted by the massive weight of surrounding rock and overlying water prevents the deeper water from vaporizing – there just isn’t enough room for the hot water to expand, even though it is really, really hot

Eventually, small steam bubbles do somehow form to rise and expand until they are too big and plentiful to pass through any tight spots in the constricted plumbing system. Here the water reaches a critical point when the confined bubbles are able to “lift” the overlying water above it. And so the geyser can now erupt.

Violent boiling results as pressure from the overlying water is decreased. Instantly, a spectacular volume of steam is produced, and it is this steam that has forced the overlying water out of the geyser vent in a superheated mass. The eruption ceases when the reservoir of water is exhausted or when the gas bubbles diminish enough to be able to rise without pushing up the overlying water.

There are geyser basins all over the park, and the one where I will spend many of my working hours this summer is West Thumb on Yellowstone Lake.

West Thumb Geyser Basin

The main references used here are:
Bryan, T.S., 1990, Geysers:  What They Are and How They Work, Roberts Rinehart Publishers.
Old Faithful Area Trail Guide and Norris Geyser Basin Trail Guide, National Park Service pamphlets available at all visitor centers!

Katherine Hanson

Hey there, I'm Katherine Hanson, the curator of watchingforrocks.com, a site dedicated to uncovering the hidden gems of the USA. With a passion for exploration and a love for discovering the beauty in every corner of this vast country, I'm on a mission to share the best cities, national parks, historic landmarks, and entertainment hotspots that the USA has to offer. From towering mountains to bustling cities, there's so much to see and experience. Join me as I embark on adventures and uncover the wonders that make America truly remarkable.
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