Soil creep

soil creep

I was up in Redwood Park this morning looking for this. Not the woods or the sun or the fine cool air, lightly scented with fall leaves. A textbook publisher wanted a photo of bent trees like these, which curve because they grew on a creeping slope. The sandstones across the Oakland hills weather into clean, fine sand that doesn’t have much strength. Thus the slopes in the redwood groves are as steep as a sandpile. Redwoods favor the sandstone because it retains moisture, and they seem to be fine with the angle of slope. But other trees root themselves differently, helpless against the very slow, steady earth movement called soil creep, and saplings may have to correct their stance as the ground shifts.

If compression across the Hayward fault didn’t keep pushing the hills up, they wouldn’t have these intimidating slopes but would soften into something more like the hills of Moraga.

The valley here is precious for being the habitat of the rainbow trout’s type population, the community of fish from which the species was first officially described. That doesn’t mean that the trout here are higher in genetic diversity, or bigger, or more special in any way except their fortuitous encounter with a biologist. But the park is taking good steps to safeguard the stream anyway, and I am so proud of East Bay voters for continuing to ensure funds for the regional park system. Developers take care of themselves; utilities and municipalities do too. Only the people, united, can take care of their common lands.

8 Responses to “Soil creep”

  1. Mark Says:

    May I ask if this is the old “Redwood Park” area of Tilden Park?

    [No, Mark, that’s in Berkeley. — Andrew]

  2. Susan Says:

    I’m guessing alders, but without any leaves it’s hard to tell. Botanists don’t go around identifying trees with no more than photos of their trunks.

  3. rebecca bond Says:

    They look like California Bay Laurel… I’m basing this on the leaf cluster in the upper left corner of the photo….

    [That is a laurel leaf cluster, but these are not laurels. — Andrew]

  4. Holly Says:

    Ah, now I get it. Thanks.

  5. Andrew Says:

    They started out as straight saplings, but the ground kept tilting them so that in staying vertical they got curved trunks. Soil creep is faster near the surface, so a vertical-rooted tree will be tilted by differential movement.

  6. Holly Says:

    I didn’t know that about redwoods liking sandy soil and tolerating creep. Makes sense, with their shallow root system. I still don’t quite understand why creep makes the other trees bend, though. Were they originally on a flat surface, and creep dragged them down to a steep slope?

  7. Andrew Says:

    I’ll bet someone does, but I don’t. Something deciduous.

  8. Silver Fox Says:

    A nice photo showing soil creep. Do you know what kind of trees they are? More than one kind?

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