Trusting Tustumena

Tustumena is the largest lake in the Kenai National Wildlife Refuge (and one of the ten largest in Alaska), three hours south of Anchorage. The Dena’ina name is reported as Chustylena or Dusdubena, meaning peninsula island lake. The greater area is known as Yaghanen, the good land.

I’ve been monitoring satellite imagery of Tustumena for years, hoping to catch a window of skateable ice. The lake is big, long, deep, and windy, all of which delay freeze up. The lake hadn’t frozen yet this winter, but a sustained high-pressure window in early March did the trick. Clear skies and cold temperatures are great for ice growth—and ice skaters!

The ‘big tell’

Tustumena is off of the road system and lacks any FAA or DOT webcams. I relied entirely on windy.com and satellite imagery to gauge conditions.

The big tell was when NASA’s daily satellite imagery revealed large green areas without any shifting—if these were bodies of open water, I’d expect to see rafts of ice or some other movement. This year’s skating season has given me a new appreciation for ‘lack of change’ as an indicator of good skating conditions.

Higher resolution imagery was available for March 3rd. Zooming in on the northern green area, I see a faint white texture on the ice. From playing this game for a while, I recognize this texture as either floating rafts of slush in open water, or cracks and pressure ridges. A closer look at the texture convinced me that these are cracks and pressure ridges bounding plates of ice—and that’s a good thing! Thin ice would just break up and blow around. The ice must be fairly thick (3 inches?) to support cracks and ridges visible from outer space.

Weather

I have no way to determine how thick the ice is from satellite imagery. So, the next part of my research was to look at the weather history and forecast to determine if the ice was likely to be thick enough to justify a visit (a three+ hour drive and ten-mile ski).

Based on satellite imagery and visualcrossing.com, I came up with this weather history (more about how to use visualcrossing):

• Feb. 26: Open water and the first formation of thin ice rafts. -10 ºF (-23 ºC) at night.
• Feb. 27: More development of surface ice due to -20 ºF (-29 ºC) overnight low temperatures.
• Feb. 28 / March 1: Snow! Darn it. Imagine the ice if it hadn’t snowed! The snow depth was probably about 4 inches (10 cm). The lake was a mix of snow-covered ice and open water, as indicated by the Sentinel 1 imagery below.
• March 4: The start of the high-pressure window: -18 ºF (-28 ºC), clear nights.
• March 5/6: Subzero temps at night and clear skies—ideal for growing ice!
• March 9: My skate day.

Based on the weather conditions, I guessed that the ice would form at a rate of about an inch (2 cm) per day until it was ~5 inches thick, then growth would slow down. This guess was largely based on a few trips to Portage Glacier (an hour from home) where I measured ice growth March 3rd and 5th. The surprising factor at Portage was how effectively snow cover was limiting ice growth, as captured in the (viral! 1M views!) video below. But that’s another story.

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Planning the outing

Given the forecast and my expectation of finding 4+ inches of ice, I started planning the trip.

Tustumena is an intimidating destination. The lake is ridiculously deep—950 feet (290 m), that’s deeper than Cook Inlet! But the real problem can be wind-generated waves. Tustumena has a fetch of 25 miles (40 km) (fetch is a measure of the longest wind corridor along the lake). Winds pouring down from the Harding Ice Field along Tustumena Glacier can build large waves quickly, and these waves have swamped boats. I found a logbook entry from three teenagers who survived a capsize by swimming two miles to shore and then hiking to a refuge cabin.

My first choice is never to travel alone, but with Sarah out of state and unavailability from my skate partners, I decided to at least make a scouting mission. If the ice was good, I could return with a crew.

Friends and friends of friends helped me decide to ski 7.5 miles (12 km) on the Pollard Horse Trail from Kasilof to Nurses cabin (built in the 1940s by two cannery nurses, $35 rental). The trail passes through the 2014 Funny River fire, a somewhat surreal passage through a burned boreal forest.

After a night at Nurses cabin, I’d ski a few more miles along the lake edge to access the northernmost body of ice and test it for travel.

The approach

The snowmachine trail was lightning fast. So fast that both trips felt like the downhill direction.

I started a fire and then sawed a dead tree near the cabin for more firewood. I had purchased a Mel’s sandwich from Odies in Soldotna and tossed it on the wood stove to reheat for dinner. Pro move 🙂

I got an early start in the morning, eager to visit the ice. After following wolf tracks along the shore, I dropped down to the lake.

The ice

The ice was thick! At least five inches … large-grained and smooth. Wow wow wow!

Science-nerd alert! I can’t help myself … there are a few really cool things going on in this photo.

1. Note the faint surface texture below the sun’s reflection. This is a trace of the original ice cover … the first crystals. This type of texture is due to ‘unseeded’ growth, meaning that there weren’t many nucleation points (specks of dust, fragments of ice crystals from the air, etc.). These first crystals were large, and the subsequent downward growth of ice maintained the large crystal geometries.
2. Check out the patches of ‘flashy’ ice visible to the left and right of the sun’s reflection. The flash is due to numerous cavities that are aligned along planes within the crystal lattice (specifically, flat cavities perpendicular to the c-axis). Each zone of flashy cavities reveals the shape of a single crystal (to be clear: a single crystal contains many cavities). These crystals are head- and arm-sized!

The cavities that create the flashy patches are known as ‘vapor figures’ (these are described on the Lake Ice site, but I found this original source easier to understand). Here’s what is going on: Absorbed solar radiation heats the ice to the point of internal melt. And because liquid H2O takes up less space than solid, the melt cavity is a mix of water and vacuum (an air pocket, but without air). Slow and uniform re-freezing would re-fill the cavities with ice, but what actually happens is rapid and not uniform, so the vacuum part of the cavity gets trapped (some of the melt must freeze inside microcracks, otherwise there would be a conservation of mass problem).

You can see the outline of the hexagonal cavities in the photo below. Note that the edges of all hexagon cavities within a single crystal are parallel, as governed by the crystal lattice. Internal melt will be worrisome later in the season, but at this point, these textures are just cool … not spooky.

I skated along the edge of the northern body of ice and encountered a number of manageable wet cracks and pressure ridges, as expected from the satellite imagery. The big surprise was that the white areas in the imagery turned out to be skateable white ice (snow that was saturated and turned to ice). With thick and continuous ice, and able to easily send updates to Sarah (unexpected cell reception), I decided to keep skating.

Part of my trip planning involved tracing the polygons of good ice in Google Earth and then importing them into the Gaia GPS app. I also had the near-real-time satellite imagery loaded in the Avenza app. After skating through a body of good ice, I’d check the imagery and find the best route to the next body of good ice.

Velvet and risk assessment

After a few hours of skating, I found myself on ice that felt like velvet. A big part of my ice safety game is paying attention to change, like re-evaluating the ice’s strength at each transition. So, I stopped to investigate what was different.

The difference was that I was no longer on large-grained ice. The photo below shows small bumps that reminded me of a basketball’s grip texture. The bumps are the crystals—tiny compared to what I’d been on earlier! I chipped a hole through the ice and noticed that it broke along skinny columns like Japanese Pocky stick treats (yes, this is a sponsorship solicitation 😉 ).

Unlike the ‘unseeded’ large-grained ice from earlier, this ice was likely seeded. My guess is that it had something to do with fog, because there was fog on the lake this morning. Maybe fog vapor droplets or small ice particles fall from the fog and nucleate crystal growth?

The presence of fine-grained ice made me stop to update my risk assessment. Whenever I’m alone, I’m more vulnerable if something goes wrong. And at this point, I was several miles from shore on a lake that shouldn’t be traveled by snowmachine and is several miles from the road system. Small-grained columnar ice is less trustworthy than large-grained—it is susceptible to rapid weakening because the grain boundaries rot out due to absorbed solar radiation (the crystals are too small for internal melting and vapor figures, so melting occurs at the grain boundaries instead). My big questions were:

1. Is this fine-grained ice getting enough solar radiation to be a concern?
2. Is the ice to the south small-grained, or is this patch an anomaly?

I didn’t know the answer to (1). A lot of this ice science is new to me, learned while creating the Wild Ice course. I’m eager to watch a thaw cycle with my new insights. But I felt fairly confident that it is too early in the season for solar radiation to weaken the ice. Standing water is a good indicator of the thaw cycle and weakening ice, but there wasn’t a hint of standing water.

I used my ice pole to test the ice’s strength, determined it was plenty strong (for now), so then moved on to question (2): Is this an anomaly or a sign of things to come? I decided to skate to the next body of smooth ice. If it was small-grained, I’d turn around.

When I reached the next body of smooth ice, I was relieved to recognize the original large-grained crystal structure. I did find more small-grained ice later in the day, but it was always thicker than in the original site and bound by large-grained ice.

White rainbow

The lake is oriented NW-SE, which means that I traced the sun’s path from the SE to the S during the morning hours. A wall of fog gave way to reward me with an incredible ‘fogbow’ or white rainbow. Surreal and super cool! (Apparently, the fine-grained fog particles don’t split the sunlight into a rainbow’s colors like raindrops do.)

I reached the southern limit of good ice after a zig-zag route of 25 miles (40 km). The southern limit was marked by cool textures where white ice had broken and re-frozen next to smooth black ice.

I returned along a slightly different route to avoid the suspect body of small-grained ice. I worked against a head wind but still made good time returning to the northern body of good ice.

I wanted to circumnavigate back to my starting point, but I kept getting pinched out by wide cracks and pressure ridges. Pressure ridges typically feel less solid in the heat of the day than they do in the morning after a hard freeze. That, combined with the fact that I was physically and mentally tired from the distance I’d covered, led me to feel more exposed than I wanted. After a strike with the ice pole revealed that I was on thinner ice than expected, I changed plans and cut directly to the eastern shore where I could retrace my route from the morning or get off the ice entirely.

Being close to shore helped me to feel less exposed and I was able to comfortably navigate the final cracks and ridges. A recording of the morning’s track was helpful to re-visit crossing points.

The snowmachine trail had fresh wolf tracks—loping! The tracks kept me entertained for the final few miles to the cabin. I hadn’t planned on a second night at the cabin, but after a 50-mile day, I was whooped. I started the fire, cooked a dehydrated dinner, made it through a few pages of my young-adult fantasy book, and was asleep by 8 PM.

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It has been a pretty rough winter. Sarah and I delayed sending holiday cards because, if we waited until January, we could announce our pregnancy. But we didn’t make it through the first trimester. And then we both got sick, and then continued to struggle in our separate ways. I doubled-down on fitness, a big part of my healing path, but wasn’t able to connect with partners. Pickup hockey was my greatest boost, despite being the worst player in our crew. But then I sliced my ankle open right before spring break, which took a ski trip off the table.

This 50-mile day was a firehose of pure oxygen, inspiration, and accomplishment that I needed, and it helped put me on a better path toward reconnection with Sarah.

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If you want to learn more about ice and traveling over it, check out Wild Ice!, my online course about all things ice! I learned a ton and really enjoyed putting this together.