The third book that changed my thinking in Denali was a book on glaciers. As a child, I couldn’t understand how the glaciers receded at the end of the Ice Age. How does ice flow back up a mountain? But that book, reinforced and deepened by hikes on some of the park’s glaciers, helped me understand what I came to call the Two Levels of Flow, an important idea in that golden book of life.
If a glacier had a medial moraine, I would hike up it. I would follow the moraine’s raised, rounded rocky path up the middle of the glacier. On the lower part of the glacier, last winter’s snow had all melted by early summer. To either side of the moraine lay the exposed hard ice of the glacier with occasional streams of meltwater flowing in ice-smooth channels that the absolutely ice-cold streams were slowly melting into the glacier. I kept to the firm footing of the moraine’s rocks.
As I ascended the moraine, the air grew cooler. The glacier grew quieter as less melt water flowed. Around me, tiny patches of snow survived within the cold shadows of large boulders. I could see up ahead where the white of last winter’s melting snow still remained. Up there at the snow line, the dark, heat-absorbing rocks of the moraine were snow-free, allowing me to keep going, but off to either side, the glacier now stretched snowy white and ominously smooth. I didn’t go walking out on that snow; it might be covering a crevasse. Whether correct or not, I felt secure on the rocky moraine. As I kept ascending, the snow to either side grew deeper, rising higher, slowly submerging the moraine until it too was covered in snow. I did not dare go further. There I would sit and rest, letting this singular location high in the company of glaciers, summits, and ridges flow into me.
If I came back a week later, I would be able to hike a little farther because more of the snow would have melted by then. The snow line would keep receding upslope as the snow keeps melting in the long summer days. But then the days grow shorter; the nights grow longer and colder. Freezing temperatures return, first within the night but then creeping out beyond the sun’s rising and setting. There comes a time in autumn when no more snow melts. The remaining snow has survived the summer and will soon be buried beneath the upcoming winter’s snow. The accumulating weight of next winter’s snow will press down on this year’s surviving snow, initiating its transformation into glacial ice. The first stage of that ice-ification is called firn.
The final high point of that summer’s snow line is termed the firn line. Downslope of the firn line, all the snow that fell the winter before has melted away, exposing the underlying glacial ice. But upslope of the firn line, not all of the winter’s snow has melted. Some of it survives so that year after year, the snows accumulate. Glaciologists call the area upslope of the firn line the zone of accumulation. It’s where, year after year, more snow falls than melts. It’s where the glacier grows. There are places in Antarctica where the glacial ice has accumulated almost 3 miles high. (That is three miles of solid ice, not fluffy snow).
Glaciers cannot be born or grow below the firn line. They can only begin above that elevation, up where the snows can accumulate year after year. Up there, however, as the snow transforms into ice, it becomes “plastic,” capable of distortion and flowing. On the steep slopes of mountains, the mass of ice starts to flow downslope. Eventually it will flow down across the firn line. Crossing the firn line is moving down into the area where more snow will melt than falls during the year. The glacier is crossing into “enemy territory” and the glacier starts to thin. (The area below the firn line is called the zone of ablation. Ablation is a scientific word that recognizes that flowing away is not the only way water leaves the glacier. It can also evaporate or sublimate off the glacier.)
However, the zone of accumulation is “feeding” more ice into the glacier than is melting just below the firn line, so the glacier can keep flowing further down into warmer air that takes an increasing toll on the glacier. There comes a place downslope where the temperatures are warm enough that all the ice will have melted by that place. That place is like the flypaper example back in general systems thinking that stops the fly from flying any further. Ice flows in but it can’t flow out because it ceases to exist as ice at that spot. That is the end of the glacier’s ice – literally. There is no more ice to flow farther down slope. This is the snout of the glacier because it looks like an ugly snout.
Up in the zone of accumulation, the glacier is mostly ice, though rockfall from the bordering slopes piles rock upon the edges. As the massive weight of the glacier slides over bedrock, it grinds and plucks more rock into it, growing ever more laced with rock and grit. Below the firn line, the ice melts and flows away but the rocks can’t. The surface of the glacier becomes increasingly covered with the rocks that were within the ice that once lay above the current surface but has melted away. Rocks become a greater percentage of what’s left within the glacier so that almost all you see at the snout is a steep slope of loose rock. The ice you can see is the ice back in the cold shadows lining the low passages at the base of the glacier, from which grey meltwater emerges from darkness into the light.
The glacier as a system has come into dynamic equilibrium. The zone of ablation below the firn line has come into balance with the zone of accumulation above the firn line. Understanding this relationship helped me understand why almost all of the mountain glaciers begin on the north sides of mountains (in the Northern Hemisphere). In the cold shadows of the north-facing slopes, very little summer melting can happen. The snow can accumulate there easily, not necessarily because lots of snow falls but because very little of it melts. Three times I have ascended an easily-climbed south-facing alpine ridge, expecting to cross and drop down the other side, only to be confronted with a sheer headwall cliff gnawed out by a glacier on the north side. (This is also why The North Face is such a great name for a mountaineering supply store.)
Understanding the relationship between the zone of accumulation and the zone of ablation also allowed me to finally understand how glaciers could recede at the end of the Ice Age. A receding glacier never flows uphill. The ice always flows downslope. What was “receding” upslope was the firn line – that line below which more snow melts than falls during a year. An increase in average summer temperatures, for example, would melt more of the glacier’s snow, moving the firn line up so that the zone of ablation starts higher. The glacier would not be able to flow so far before all the ice had melted away.
The firn line could also move upslope if less snow fell during the winters. The summer temperatures might remain the same but less snow is falling so at the former firn line, the snow that falls would be melted before the end of summer, giving the summer temperatures a bit more time to start melting the ice beneath so that place is no longer the firn line. The firn line moves upslope.
A movement of the firn line upslope shifts the dynamic equilibrium between the zones of accumulation and ablation. Less of the glacier is in the accumulation zone; more of it is in the ablation zone. The glacier can’t flow as far. The lower end of the glacier melts away and comes to its end further upslope. What recedes uphill is the snout, the point where all the ice has melted, not the actual ice flowing within the glacier.
The snout and firn line are not the same thing as the ice within the glacier. The ice always flows down. The firn line and snout can move upslope or down, depending on which is greater: the glacier’s inflow of snow or outflow of melted water.
Thinking about this difference as I hiked the park led to the idea of The Two Levels of Flow. The ice within the glacier was the lower level, the level where the actual flowing is happening. The glacier with its snout was the upper level expression of that flow. A more familiar example is traffic. Traffic backs up at a stoplight – even though none of the cars within the traffic are backing up. The cars are the lower level of the flow; the traffic is the upper level expression of that flow. These are another “3D” example that challenges the mind to hold two different views of the same reality in focus at the same time. When we can do that, we see more dynamic change. A river in flood rises even though its water is flowing down towards the sea. The water is the lower level of flow; the rising height of the river is its upper level expression.
The relationship between the two levels is shaped by the simple logic of what I came to call the Rules of Flow.
First: If the rate of inflow is greater than the rate of outflow, the upper level expression accumulates.
Second: If the rate of inflow is less than the rate of outflow, the upper level expression diminishes.
Third: If the rate of inflow is equal to the rate of outflow, the upper level expression remains the same.
The difference between inflow and outflow is relative. I can increase my weight by eating more or exercising less. What shapes the upper level expression is the relative balance between inflow and outflow. Which is greater? I can increase my wealth by increasing my income above my expenses or by reducing my expenses to be less than my income. A glacier can diminish if less snow falls in the winter or if more snow melts in the summer. The temperature on Earth is the upper level expression of heat flow. Heat is always flowing from the Earth out into space but during the day, the inflow of solar energy is greater than this outflow; the sunlit portion of the Earth accumulates heat and warms up. When we are spun into the Earth’s shadow, the inflow ceases, the outflow of heat continues, and the upper level expression of temperature declines throughout the night. What I’ve come to call The Relative Balance between inflow and outflow is the key to what happens to the upper level expression of that flow.
This distinction is profound. It’s one of the keys to reading whatever part of that golden book of my dream I’ve been able to read. I had been learning in Big Bend and Denali to think of everything as flowing. Seeing flow from the different perspectives of the two levels led to a deeper understanding.
If inflow equals outflow, a dynamic equilibrium forms that’s often stable over time. Our body temperature of 98.6º, for example, is an upper level expression of internally-generated heat flowing out into the surrounding air. This temperature is not fixed; it’s a dynamic equilibrium that fluctuates throughout the day. If we get too hot, we sweat to create evaporative cooling. If we grow too cold, we shiver in order to generate heat. 98.6º is the balance point of a dynamic equilibrium that lasts our lifetime.
If one does not look closely, the upper level expression of a balanced flow can seem unchanging, like the level of a lake. We can think this upper level expression is an eternally-fixed given that can be taken for granted. But everything is flowing. Things we might take for granted (mountains, buildings, soil, highways, aquifers, companies, beaches, economies, forests, families, our atmosphere) are actually upper level expressions of flow. Change a relative balance and any upper level expression can take on a new shape or dynamic as the lower level accumulates or flows away.
Almost all of our environmental problems can be traced back to our changing a sustainable relative balance underlying something we took for granted. If trees are cut down faster than they can grow, a forest will fade away. Many of the world’s lakes are drying up because much of their inflows has been diverted to irrigation. Increased greenhouse gases reduce the rate of heat outflow from the Earth and the Earth’s temperature begins rising.
The development of chemistry revealed the dynamic recombining of molecules, a pervasive flow of ever-changing molecules shaping our world. Upper levels are all we tend to see until we learn to see the sustaining flows beneath them. When I focus on the interplay between the upper and lower levels and the Rules of Flow, I start seeing more connections. Every inflow I see also becomes some other place’s outflow. Every outflow I see is simultaneously becoming some other place’s inflow. Flows connect places into networks. I am, for example, upstream of the Great Pacific Garbage Patch.
Everything is flowing. Assume that nothing can be taken for granted; nothing is an immutable given. The upper level expressions of the world depend on the relative balances between rates of flow. I grow sensitive to rates which are how fast something changes or flows through Time. I grow more precise in my awareness of time, the fourth dimension.
I mark things to help me understand rates. Walking along a beach as the tide receded, I come upon a small stream seeping from the cliffs and disappearing into the sand at a certain point. I mark this point. On my return later, my marks reveal that the stream no longer flows as far. It has receded ten feet up the beach. Why?[1]
Preparing to eat my lunch high in the mountains on a hot summer day, I place a rock at the edge of a snowbank to mark how fast the edge of the snowbank will melt in the time it takes to eat my lunch. The recently-excavated dirt around a gopher mound stands higher and “fluffier” than an older mound, revealing how the mound will gradually compact through time. South-facing slopes melt off faster in the spring than north-facing slopes. Bare talus slopes slide faster than vegetated talus slopes. This year’s fallen leaves decompose faster in some places than in others.
As I
grow more aware of change, I hold “then” and “now” together in my mind in
another “3D” example
and a palpable sense of flowing through time develops. Every moment is one
frame of an ongoing movie. As I practice seeing the two levels of flow, I start
seeing the movie.
[1] Reason for the receding beach stream:
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