Monday, September 2, 2013

Scratching the surface

photo of St. Croix Falls bedrock
© harrington
Happy Labor Day! Thanks for stopping. We're on the downhill slope of the Where you at bioregionalism quiz. Today we're working on question     "16.    What primary ecological event/process influenced the land where you live?
 (Bonus special: what’s the evidence?)" Since geology isn't my specialty, my answers come from a variety of resources but primarily Minnesota's Natural Heritage by John Tester and Chisago County's SURFICIAL GEOLOGY By Gary N. Meyer (2010). From the latter, we learn that:
During the last glaciation, the Michigan Subepisode, Chisago County was repeatedly covered by ice carrying debris of Superior provenance, the Superior lobe (the line of maximum extent is dotted where covered by the Des Moines lobe). After the final retreat of the Superior lobe, the Grantsburg sublobe of the Des Moines lobe, carrying debris of Riding Mountain provenance, moved into the county from the southwest, covering it with ice one last time.

Glacial sediments deposited in the county derive their distinct material content from bedrock and sediment found in the region of these provenances (source regions).
For the Bonus Special, note that in addition to the sediment deposit evidence, the Minnesota/Wisconsin border is just down Highway 8 where we can visit Taylor's Falls and Interstate Park. The geology of the park, particularly the glacial potholes found in the park, reflects much of the effect of glaciation in the area. (Side note: the question is phrased in the past tense. It won't be too long, in my opinion, before the emphasis shifts from glaciers and geology to climate and vegetation.) This poem by Bob King seems to fit nicely with today's answer.


By Bob King
I know the origin of rocks, settling
out of water, hatching crystals
from fire, put under pressure
in various designs I gathered
pretty, picnic after picnic.

And I know about love, a little,
igneous lust, the slow affections
of the sedimentary, the pressure
on earth out of sight to rise up
into material, something solid
you can hold, a whole mountain,
for example, or a loose collection
of pebbles you forgot you were keeping.
Thanks for listening. Stop by again when you can. Rant's, raves, and reflections served here daily. Frequently  with a side of poetry. Oh, in case you're looking forward to tomorrow's question, it's
"17.    What species have become extinct in your area?"
See you then?