Mt. Nusatsum

Mt. Nusatsum

Tuesday, February 1, 2011

Repost of Glaciers and Gravestones

 Last winter I posted this, and a number of readers enjoyed it.  I'm on the road tonight, so can't tell you much about the Bella Coola Valley, some readers may not have seen this post.  Grizzly

You might not know it, but dying in Bella Coola and being buried in our pretty little cemetery  can make a real contribution to the study of glaciology and the relation to the climate shift debate that is happening.  Everyone seems to be in in agreement that glaciers like the one in this photo are generally getting smaller, and we've all watched the ones we can see from roads around Bella Coola shrinking over time.

In the late 90's some researchers were looking at the period known as the "Little Ice Age" which was a cooler period in this area beginning in the 13th century.  This period saw glaciers advancing in the 13th and 14th centrury, taking a break, then advancing again in the 17th and 19th centuries and finally ending in the 20th century.  While a lot of interest and research has gone into determining more about the extent of this Little Ice Age, researchers are always looking at ways to more accurately determine when a period ended.  In the case of the end of the Little Ice Age in this area, one method has been to examine glacial moraines adjacent to glaciers and the vegetation growth on these (mostly trees) to determine when these areas became ice free by aging the trees.  It's common to use the technique of dating trees that grow on the moraines, but some moraines take 100's of years for trees to colonize that could be useful for dating or the altitude is too high to ever see trees useful for dating.

A technique of dating called lichenometry exists where the growth rate of lichens on exposed rock is measured and then the age of the lichen is determined and thus working backwards arriving at when the rock become exposed (from the ice or glacier).  One of the challenges with this method is that lichens grow at different rates in different areas and different species.  Clear headed, clever researchers who spend a lot of time breathing clean mountain air and looking at glaciers in the Coast Mountains and especially the areas around Bella Coola figured out that they could use the Bella Coola Cemetery to help them determine the date of glacial retreat.   By finding gravestones of natural rock, with lichens on them (Rhizocarpon geographicum) which grow on rocks at altitudes and in the cemetery, the rocks exposed recently near glaciers could be dated.  They simply compared the size of the lichens on the rocks with the size of the lichens from gravestones in the Bella Coola Cemetery.  This lichen species can become 100's of years old and by measuring the diameters can be used to age the rock exposure time.

Turns out these researchers used 9 different gravestones in the Bella Coola cemetery to develop the "Bella Coola Lichen Curve" (go ahead type it into Google if you don't believe me), which is simply a line on a graph plotting age vs size (diameter).  Since the Bella Coola Lichen Curve was developed most glaciologists working in the area refer to it in their studies or calibrate their own data against it, to age areas which are ice free near glaciers and thus start to determine when areas became ice free. Of course the longer the period we have data on the melting and advancing of glaciers will help bring more facts and science to climate discussions.

One thing I'm certain on--make sure they use a big rock for my gravestone, I want to make my contribution to future climate studies long after I'm gone.  Grizzly

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