Note: As of September 22, 2020, earthcachers are required to post a photo of themselves at/on the drumlin with their log. Since June 2019, mandatory photo requirements have been permitted under Earthcaching rules, as long as they complement other well-developed logging tasks. This requirement is to ensure cachers actually make the trek to the island. You are not required to show your face in the picture; a photo of your GPSr or a personal item will suffice.
In dry years, you can walk from the east shore of the lake all the way to the island without stepping on any ice. Be prepared to use a watercraft if need be, but boots and/or waders may be all you need. Begin at the posted coordinates and walk or snowmobile up to the summit.
From above Birch Lake, drivers on the Yellowhead Highway can look down and see an island rising up from the lake’s shallow waters. This island is actually a drumlin – a visually distinctive landform created by glacial activity.
Drumlins are elongated hills that are recognizable by their distinctive steep and gradual slopes at their respective ends. They are composed largely of glacial till – rocks and sediments transplanted across distances by advancing glaciers. As glaciers advance across the land, they scoop up (“scour”) all manner of soil, rock, and organic matter. When the glacier stops advancing and melts, the material it has been carrying is deposited in that new location.
Drumlins vary in shape and size, but certain patterns can be consistently observed. As mentioned earlier, they have a distinct steep slope at one end (stoss), and a much more tapered slope at the opposite end (lee), such that the overall shape can be likened to an upside-down teaspoon. This long axis of the drumlin is parallel to the direction the ice flowed, with the tapered end pointing in the direction the glacier was advancing. It is important to note that glaciers only move forward; they never move in reverse. When glaciers are said to be “in retreat”, it means they are melting at a faster rate than their forward progress, giving the appearance of retrograde motion as the leading edge of the ice (the ‘toe’)“moves” back.
Though they have been studied for over a century, there is still debate as to how exactly drumlins form. The two main hypotheses endorse either a constructional (material under the glacier is moved and manipulated into shape) or erosional (meltwater or ice erode material under the glacier into a distinctive shape) process as being responsible. The most contemporary understandings suggest they are formed by a combination of the two processes. One hypothesis suggests that as an advancing glacier is obstructed by erosion-resistant rock, the glacier must rise quickly above the rock in order to continue moving forward. This rapid ascent causes till to be deposited in a steep formation, until the ice surpasses the height of the rock. From here, the glacier can continue moving forward past the rock, depositing till at a gradual rate as it descends and giving the drumlin its distinctive shape (see below).
There is no “typical” size of drumlin. They may range from 250 m to a few kilometres in length, 100-500 m wide, and 5-50 m high. The size depends on the amount of material and the number of times the glacier advances over that same spot (recent analysis of drumlins revealed by the retreat of the Hofsjökull glacier in Iceland has demonstrated that different layers of till in a drumlin are formed by multiple distinct surges of the glacier). But regardless of its size, a drumlin’s dimensions tend to follow a width-to-length ratio of around 2:3.5.
Although they are primarily composed of till, drumlins are not exclusively such. The “core” of a drumlin may be bedrock, sand, boulders, clay, or other materials, with layers of till deposited on top. Interestingly, the till material is very local – that is, the material has been scoured, transported, and deposited over a relatively short distance.
Drumlins may appear in isolation, or they may appear as part of “swarms”, hundreds or even thousands strong over a vast area. The drumlin of Birch Lake is solitary, although another, smaller one is visible on Kenilworth Lake, 70 km east along the Yellowhead.
Sources
- McKinnon, Mika. Drumlins are the easy-to-identify, hard-to-understand glacial landform. 2015 March 03. <http://space.gizmodo.com/drumlins-are-the-easy-to-identify-mysterious-to-unders-1692890209>
- As Physical Geography - Drumlins, posted by A Level Revision. <https://www.youtube.com/watch?v=RyKmLINrRAg>
- http://www.britannica.com/science/drumlin
- http://www.landforms.eu/Lothian/drumlin.htm
- http://www.geography-site.co.uk/pages/physical/glaciers/drum.html
- https://en.wikipedia.org/wiki/Drumlin
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To log this earthcache as found, first e-mail me the answers to the first four questions (don’t post them in your log!). You may log it as found without hearing a response from me, but e-mails with missing or poor answers may be deleted, and the cacher notified as to the reason(s) why.
1. Mark a waypoint at the drumlin’s summit (so you can begin to peer over the edge; don’t go too far!). Project 72 m at 228° and call that one Waypoint A. Calculate the distance between Waypoints A and B (provided). Also calculate the distance between Waypoints C and D (both provided). Compare the drumlin's width to its length. Does it roughly equal the dimensional ratio described above?
2. What is the name of the slope you can view from the summit?
3. Estimate how high the drumlin’s summit rises above Birch Lake.
4. In which cardinal direction was the glacier advancing when this drumlin was formed?
5. Post or e-mail a photo of yourself, your GPSr, or a personal item at the top of the drumlin or at the bottom of the “cliff”. This requirement is mandatory.
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FTF: billy robson