EGU Blogs

The Accretionary Wedge #58 – Signs

For this AW I had originally drawn a blank. I don’t have that many pictures of signs in my photo collection and most of them really aren’t that interesting anyways. However, I was struck by a flash of inspiration on a hike in Gatineau Park last night. My girlfriend and I were doing the beautiful King Mountain trail plus a nice add on loop that took us off the beaten path as well. While doing to the King loop though, we came across an interesting sign that I thought would be worth sharing and make a nice contribution to July’s Accretionary Wedge at Georneys.

(Photo: Matt Herod)

Canada’s very first geodetic reference point! It is a now a national historic site. (Photo: Matt Herod)

The sign/cairn pictured here shows the location of the very first point in the Geodetic Survey of Canada in 1905. The site is now a national historic site as well as one of practical value. Geodesy today is much more complex than it was in the past, but the basic aims remain the same. The purpose of geodesy is to measure and describe the shape of the Earth, called the geoid, and understand the factors that affect its shape such as glaciations, tides, and gravity. In order to do this most countries have developed a geodetic network that defines the precise position and elevation of a variety of reference points. These points can then be used to characterize the shape of the earth very precisely as well as observe any changes that could result due to changes in the Earth’s gravity field or isostatic uplift.

Geologists rely very heavily on geodesy in order to make maps, plot samples, investigate climate change, do geophysical work, hydrogeology, etc. The list goes on and on for why geologists depend on geodesy and why these two disciplines are extremely interrelated. It is not only for applied geology that geodesy is relevant though. Most of us use geodesy and benefit from its contributions daily. The big one that I am sure everyone is familiar with are global positioning systems aka. GPS, which use the coordinate systems and geoid provided by geodesy to navigate.


A close up of the information plaque. In both official languages, of course. (Photo: Matt Herod)

There was a pretty nice view from the cairn. (Photo: Matt Herod)

One great example of geodesy in action is how by using the control network of points around Canada the geodetic survey of Canada has been able to plot how much certain parts of the country are rising or falling due to isostatic rebound.

Next time you are reading a map or listening to instructions from your GPS, think about the field of geodesy that made the whole thing possible.




Matt Herod is a Ph.D Candidate in the Department of Earth Sciences at the University of Ottawa in Ontario, Canada. His research focuses on the geochemistry of iodine and the radioactive isotope iodine-129. His work involves characterizing the cycle and sources of 129I in the Canadian Arctic and applying this to long term radioactive waste disposal and the effect of Fukushima fallout. His project includes field work and lab work at the André E. Lalonde 3MV AMS Laboratory. Matt blogs about any topic in geology that interests him, and attempts to make these topics understandable to everyone. Tweets as @GeoHerod.