Lynn Headwaters Spring EarthCache

Fresh clear drinking water comprises a mere 0.003% of our planet’s water supply so we tend to be rather opinionated about how and where we obtain it. One source of water supply that appeals to a small minority of devotees is what they ardently refer to as “natural” or “living” water. The rest of us know it as spring water, and here in Lynn Headwaters Regional Park we have a small example of a natural spring.

Our dramatic and beautiful coastal landscape is the result of hundreds of thousands of years of geologic activity. The landscape of the Lower Mainland has been shaped by tectonic, glacial, and fluvial processes. The tectonic process of oceanic crust subducting beneath continental crust poses a threat of damaging earthquake and associated hazards such as soil liquefaction and slope failures. Past glaciers have sculpted the landscape into steep-walled valleys and deposited thick layers of sediment. These steep slopes are potential sites of mass movements of soil and rock, as illustrated by the massive scree field in along the Hanes Valley Trail and last December’s rock slide on the Seymour River.

The setting of the Lower Mainland in general reflects a complex tectonic evolution, but is unusual in that it is at a junction of three very different regional 'basement' complexes. The western member of this regional basement is a terrane called Wrangellia, a composite of old (about 400-150 million years) igneous and sedimentary rock types that were joined to the North American western margin about 100 to 150 million years ago. Remnants of Wrangellia now make up most of Vancouver Island, the Queen Charlotte Islands, and some portions of the western part of the Lower Mainland. The southern basement of the Lower Mainland is termed the 'Northwest Cascades System', a complex series of oceanic, volcanic, and sedimentary rocks. The northern basement rocks are the southern extension of the Coast Mountains. These are dominated by granitic rocks which formed mostly between about 175 million and 60 million years ago, several kilometres to tens of kilometres below the surface. They have been exposed mostly in the last 10 million years by a period of major uplift and accompanying erosion. Two thick sequences of sedimentary rocks overlie these regional 'basements' and in turn are overlain by younger glacial and modern sediments. These sedimentary rocks occupy two old sedimentary basins in this area. Rocks of the oldest sedimentary basin comprise the Nanaimo Group, a succession of marine and non-marine sandstone, conglomerate, mudstone, and significant coal deposited about 90 to 65 million years ago in a basin that broadly coincides with the present Georgia Depression.

Rocks of the Nanaimo Group are exposed in Stanley Park and North Vancouver and dip gently to the south beneath the Fraser River delta, reaching a thickness exceeding 1300 m. Overlying the Nanaimo Group in the Lower Mainland is a succession of sedimentary rocks termed the Huntingdon Formation, part of the Chuckanut Basin. This non-marine succession of sandstone, conglomerate, and minor mudstone was deposited between about 58 million and 35 million years ago by river systems in a basin controlled by regional strike-slip faulting . These rocks are exposed on the northern edge of greater Vancouver in areas including Burnaby Mountain, Kanaka Creek, and Sumas Mountain. These sedimentary rocks also provide the foundation material (along with a thin veneer of glacial sediments) for the buildings of Vancouver and Burnaby. The Huntingdon Formation is at least 2 km thick beneath much of the Fraser River delta, overlying the Nanaimo Group and overlain in turn by a thin, discontinuous succession of unnamed sedimentary rocks and by ice age and modern sediments. The sedimentary basin in which the Huntingdon Formation was deposited was larger than the present Fraser Lowland, extending to the south beneath the Nooksack plain and making up the Chuckanut hills in the Bellingham area (where the rocks are termed the Chuckanut Formation).

The fluvial aspect is the natural erosion of rivers and creeks like Lynn Creek, where they carve their path through the glacial sediment fields, depositing their fertile bounty downstream where man can make use of it. Thick sediments deposited by retreating glaciers contain valuable groundwater aquifers and it is one such aquifer that feeds the spring you have come to see. Between 25,000 and 10,000 years ago, glaciers in the Cordilleran Ice Sheet were responsible for carving out deep U-shaped valleys all across our area. Lynn Headwaters Regional Park is just one example. As we look around we can begin to spot many more, including coastal fjords: the Sea-to-Sky route, Indian Arm, even Burrard Inlet itself, Harrison Lake, and so on.
(Sources: Fraser River Delta, British Columbia: Issues of an Urban Estuary; by Groulx, B J (ed.); Mosher, D C (ed.); Luternauer, J L (ed.); Bilderback, D E (ed.); Geological Survey of Canada, Bulletin no. 567, 2004)

Here in Lynn Headwaters, this little spring likely would have gone completely unnoticed if not for the arrival of the mining and lumber industries. One of the side effects of the glacial activity was exposing veins of resource-rich ores on the mountain slopes. When logging companies discovered the vast old-growth forests across the North Shore, miners soon followed. Zinc and copper were discovered in abundance in the Upper Lynn Creek area and all this commerce demanded that roads be built to get the resources out. I’m sure nobody really noticed the little trickle of water when the first logging road was cleared in the bush, but today, the spring has achieved a minor celebrity status locally.

Take a look at the exposed earth around the spring. You will notice that the water appears to be gurgling up through ordinary dirt. The flow is constant enough that it is clear, not cloudy, but there is no obvious crack or portal for the water to flow through. This is typical of the glacial sediments in valleys like this. A jumble of dirt and rock, swept down from higher up in the valley and deposited here over thousands of years, seemingly solid and impenetrable, yet the inexorable actions of groundwater seeking a path to freedom has found a way through.

The following table shows a scale for measuring spring flow:

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