Geological History of the Manuels River
The rocks along the Manuels River range from 500 to 600 million years old and are among the oldest rocks in the province. These rocks are remnants of the ancient African continental plate that collided with North America 400 million years ago. The mountain ranges of eastern North America, particularly the Appalachian Mountains, were formed by the collision of these plates during that period in the earth's history. The Manuels River lies on the eastern edge of these ancient and largely eroded mountains. Nearly 200 million years ago, modern Africa started to separate from North America to form the present-day Atlantic Ocean, leaving the Avalon Peninsula behind as a remnant of ancient Africa.
The Manuels River valley is relatively young in geological terms. The original valley was shaped during the last ice age by a glacier flowing northward over the valley into Conception Bay. The melting of the glacial ice more than 10,000 years ago, left rock debris strewn throughout the area and the rivers formed by the melting ice carved the gorge and riverbed located in the lower portions of the river valley.
Originally, the river had a largely natural watershed area of approximately 75 square kilometers but hydro diversion projects in 1932 and 1956 reduced the watershed area to approximately 15 square kilometers. During times of high run off water from the original watershed spills into the Manuels River system resulting in highly variable flow rates, particularly in the spring.
To learn more about the geological and glacial history of the Manuels River, see the Geology in Depth section.
Generally, sedimentary rock types predominate in the lower Manuels River valley while igneous and volcanic rock comprises the upper reaches of the valley.
Sedimentary rock: Most of the rock types seen along the lower Manuels River result from the erosion, transport and deposition of sediment from pre-existing surface rocks. Water, wind and ice transport sediment. Water and wind are able to sort sediment into uniform particle sizes, but most sediment deposited by glaciers is poorly sorted. Sediment becomes rock over time by burial below younger deposits. A sedimentary rock with fragments the size pebbles or cobbles is called conglomerate. Sandstone, siltstone and shale are successively finer grained sedimentary rock.
Igneous rock: Igneous rock crystallizes directly from molten rock, called magma. Granite solidifies at depth giving large crystals. Volcanic rocks are usually finer grained because of rapid cooling of lava at the surface. There were active volcanoes in the Manuels area 620 million years ago. Some volcanic eruptions are explosive; hot lava fragments and ashes fall around the volcano, with some settling below water to form more stratified deposits.
Metamorphic rock: Metamorphic rocks are those which have been altered by heat, pressure and/or chemical solutions within the earth. Any rock can undergo change in composition if it is buried deep enough or exposed to chemical solutions, such as from a nearby body of molten rock. Slate is an example of a metamorphic rock, being a slightly metamorphosed shale, and marble is actually a metamorphosed limestone. Metamorphism can produce economic minerals; with perhaps the best known example being the creation of diamonds from carbon deposits. Gold, copper, zinc, and many other minerals can be formed in rocks during metamorphism.
Rock Layers: Succession and Structure
Sedimentary layers (beds) are deposited one on top of the other to form a 'succession', with the youngest on top. Stresses in the crust later cause tilting of the succession. The rocks of the Manuels River dip down to the North-North-West and so lie at great depth below Bell Island. The ironstones that were mined there are 20 million years old and therefore higher up the succession then the rocks at Manuels River.