Falls of Dochart EarthCache
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Breadalbane is home to the Ben Lawers National Nature Reserve while about 25% of the Loch Lomand and The Trossachs National Park also lies within the Breadalbane area. Nature lovers will find a landscape shaped by geology and ice, populated by giant trees and rare arctic and alpine plants, and inhabited by majestic birds and animals such as golden eagles, ospreys and red deer.
Published with the Permission of Scottish Natural Heritage.
As its name indicates Breadalbane ("the high ground of Scotland") lies wholly in the Scottish Highlands, north of the Highland Boundary Fault. The ancient rocks of the Breadalbane area were deposited as sand, mud and limestone several hundred million years ago, probably between 740 and 515 million years before the present day. Some boulder beds, notably on the mountain Schiehallion, represent glacial deposits from a worldwide glaciation that occurred about 700 million years ago. About 600 million years ago, basaltic lavas flowed over much of the sea floor. This Dalradian rock sequence, as it is known, was deposited on the eastern margin of a large continent, most of which is now North America.
About 450 million years ago, in the early part of the geological time period known as the Ordovician, the Dalradian rocks of the continental margin collided with oceanic and volcanic island arc rocks on the present day south east. This collision, known as the Grampian Orogeny, resulted in intense folding and thrusting of the Dalradian rocks and metamorphism of the sand, mud and limestone into quartzite, schist and marble. The metamorphosed limestone has been worked to provide fertilizer and evidence of lime kilns can be seen in many places. Over most of Breadalbane, south of Glen Lyon, these metamorphic rocks are relatively flat-lying. The unusual thing about them, however, is that as a result of folding they are upside down! The next major geological event to take place occurred in Silurian to Early Devonian times when the metamorphic rocks of the Grampian Highlands were displaced by a series of major faults.
In Breadalbane these include the Tyndrum, Bridge of Balgie and Loch Tay faults. You can see the evidence of the Tyndrum Fault on the hillside SW of Tyndrum where the vein that filled the fault produced thousands of tons of lead plus associated zinc and silver at various times between 1741 and 1862. An offshoot of the Tyndrum Fault in the Cononish glen may shortly go into production as Scotland's only gold mine. The evidence of the Loch Tay fault is also clear on any map, as glacial erosion along the line of the fault has created the "bend" in the central part of the loch where the water depth is greatest.
Minor movements can still occur on these faults, the most recent being a 2.7 Richter local magnitude event at a depth of 5.4 kilometers on the Bridge of Balgie ("Killin") fault in Glen Lochay on 20th January 2005 and a smaller 1.8 event, which was heard as well as felt, at a depth of 2 km about 3 km north of Killin on 31st October 2011. The southern boundary of Breadalbane is defined by the Highland Boundary Fault, a major SW-NE trending dislocation which runs from Achill Island on the west coast of Ireland to Stonehaven, south of Aberdeen.
Movements on the fault have occurred in historic times and in the 19th century a series of movements on the fault, or minor associated faults, resulted in the construction of a building to house one of the world's first permanent earthquake recording instruments (seismometer) at Comrie. You can still see a working seismometer at Comrie's Earthquake House. Lochan nan Cat from Ben Lawers e most obvious features of the Breadalbane landscape, however, result from the much more recent Pleistocene glaciations of the past 1.6 million years. Ice-sculpted mountains with large corries, U-shaped glens and elongated loch basins all attest to the abrasive effects of ice while glacial deposits abound in the hummocky moraine deposits that occur throughout the region and the rather more unusual dried lake bed that lies in Glen Dochart between Ledcharrie and Lix Toll, SW of Killin (source: www.killin.net)
When taking a look at the stones near the Falls you will recognize some holes in the stones. These so called Potholes are cylindrical holes drilled into the bed of a river that vary in depth & diameter from a few centimetres to several metres. They’re found in the upper course of a river where it has enough potential energy to erode vertically and its flow is turbulent. In the upper course of a river, its load is large and mainly transported by traction along the river bed. When flowing water encounters bedload, it is forced over it and downcuts behind the bedload in swirling eddie currents. These currents erode the river’s bed and create small depressions in it. (source: geographyas.info) In the picture above you can see the how this "drilling process" works.
TO LOG THIS EARTHCACHE
Please send me the answers to the following questions BEFORE LOGGING via my profile email or message center
If you don't send me your answers before logging, I may delete your log!!
1. Take a look at the described holes (potholes) in the stones near the falls
a) estimate their dimensions, are they always same in size?
b) Look for the forms of the holes, do they always look like eggs? Why could that be?
2. During which time period did the collision of the Dalradian rocks of the continental margin, with oceanic and volcanic island arc rocks occur?
3. OPTIONAL: Take a picture of you and your GPS standing on the bridge with the falls in the background
If you have send me the answers youre directly allowed to log, if there are any problems with the answers I will contact you!
Happy Caching and enjoy the beauty of this magic place!
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