Blueberries and Granite

We didn’t bring enough food into the mountains. We were helicoptered in for three weeks, but after one week, we discovered that we had eaten half the food. So by the beginning of the third week, we were on pretty short rations. When another research group arrived, on schedule, to share dinner with us, things could have gotten ugly. But they didn’t, because our visitors brought instant cheesecake, and we were camped on granite in Alaska.

And granites plus recent glaciation meant blueberries.


(Source: Maine State Berry)

I grew up in Maine, so that’s one wild food that I recognize – and eat, whenever possible. Blueberries are cultivated, even commercially grown, frozen, and sent to grocery stores around the country. But the best ones, in my not-so-humble opinion, grow wild on the barren granitic soil of coastal Maine.

Blueberries are difficult to cultivate, because they thrive in very acidic soil. And that’s why they are found on granite. Natural rainwater is somewhat acidic, due to dissolved carbon dioxide from the atmosphere. Natural soil water can have an even lower pH, due to the formation of organic acids during the decay of vegetation. The rock fragments that make up the rest of the soil can serve as chemical buffers as they weather – calcite (the active ingredient in Tums) dissolves and neutralizes acid, and other minerals consume hydronium ions as they break down by hydrolysis. But quartz doesn’t. It doesn’t dissolve very readily in surface waters, and when it does, it forms a very weak acid. It certainly is no good at neutralizing rainwater or soilwater (or the acid rain that we worried about in New England in the 80’s). And granite contains a lot of quartz. So granite is no good at neutralizing acids.

But it is very, very good at growing blueberries.

Coastal Maine, north and east of Acadia National Park, is intruded by granite after granite, formed during the middle period of Appalachian mountain-building. Several hundred millions of years later, it was scraped clean by continental glaciation, and since then it’s been doing its darnedest to develop something vaguely resembling soil. (If you haven’t guessed: yes, I have attempted to garden in New England. Yes, I have harvested many rocks. Can you guess why I am a geologist and not an agricultural scientist?)

It’s a lousy place to grow corn. Or broccoli. Or, well, most things. But the thin, acidic soil is exactly what the wild blueberries love.

In coastal Maine, the blueberries are harvested commercially. But I’ve worked around the margins of granites in Alaska and Vermont, and I can tell you: the blueberries grow on all of them. If you know the geology, and you look carefully, you can find them.

And then, when you run out of food, you can eat blueberry cheesecake.

(For The Accretionary Wedge #3, Rocks and Life, hosted at The Other 95%.)