The Dead Falls – Döda Fallen

The Dead Falls –
Döda Fallen
För ca 7 000 år sedan bröt älven en ny fåra och de kända fallen Stora och Lilla Helvetet samt Södra Helvetet torrlades. Handikappvänlig promenadstig finns iordningställd för att du ska kunna tjusas av detta naturens verk. 9 700 years ago
1. South Hell
2. Little Hell
3. Grat Hell
4. Goat Ridge
5. Great Rapids
6. Högbo
7. Little Rapids
8. The Dead Falls
9. Lindsnäs
A. Old course of river at Dead Falls
B. Goat Ridge
C. Present level of river
D. Badelunda esker (ridge)
E. The probable river bed before the ice-age
F. Varves
G. Moraine
H. Mouth of sub-glacial river
I. Bedrock
J. Esker
K. Rembo
This is how it may have looked about 9 700 years ago in the area ground what is now Avesta. The ice cap was still moving slowly forwards, i.e. towards us, but the actual edge of the ice was retreating a few hundred metres northwards every year as a result of the rapid melting and of the calving of icebergs. Melt water from the surface of the ice cap ran down into numerous crevices and collected in a tunnel and crevice system hundreds of kilometres in length to form a mighty river under the ice. This river carried boulders, stones, gravel and sand to the mouth where the material was deposited in the form of an esker or ridge. Further out to sea, the finer material settled on the bottom and made each year a still discernible layer, a varve. These annual varves, together with scratches on the rocks, stage, it stretched from Avesta to Rembo as the block diagram and sketch map show. Approximately 15 years earlier, the inner tongue of the bay with the mouth of the sub‐glacial river was at the level of the Dead Falls. 8 200 years ago B. Goat ridge
D. Badelunda esker (ridge)
F. Sediment, varves
G. Moraine
I. Bedrock
J. Boulders and pebbles
L. Mattsbo heights
L. Mattsbo heights
D. Badelunda esker (ridge)
Approximately 1 500 years after the melting of the icecap in the Avesta area, additional sedimentary material settled on the sea bed. During this period, too, the land mass which had been pressed down by the weight of the ice‐cap rose up so that the higher parts of the Avesta region, including Mattsbo Heights and the esker now lay above sea level. A narrow bay of the sea still stretched up to and past Hedemora through a narrow gap between these high points. 7 800 years ago
B. Goat ridge
D. Badelunda esker
F. Sediment, varves
G. Moraine
J. Boulders and pebbles
I. Bedrock
A few hundred years later, the land had risen still higher and the sea had retreated to the level of the Krylbo area. In the previous sound at Avesta, the river Dalälven had cut down (eroded) into the loose sedimentary layers. These were soon eroded down to the bedrock which was not so easily worn away. Downstream of Goat Ridge, the bedrock sloped steeply and a rapid formed here, becoming higher and higher as the land rose. 7 000 years ago
3. Great Hell
4. Goat Ridge
The rapid turned eventually into a 15 metre high waterfall. The "outer curve" still consisted partly of shallow stretches of rapids but closer to Goat Ridge where "Great Hell" is today there was a very steep waterfall. Most of the flow was concentrated into a channel in the bedrock. The interior of Goat Ridge consists of a core of rock covered with loose overlying sediment. Part of the water from the fall eroded back around the steep rock cliff of Goat Ridge's north side at the same time as the powerful current above the fall eroded in sideways (see the 2 arrows on the illustration above). Goat Ridge became more and more isolated from the rest of the shore. 7 000 years ago
B. Goat Ridge D. Badelunda esker F. Sediment G. Moraine I. Bedrock J. Boulder and pebbles
B. Goat Ridge
Approximately 7 000 years ago, the great waterfall collapsed. The river cut a new channel north of Goat Ridge, probably in connection with a spring flood. The illustration shows a situation which may have existed a very short time, perhaps less than one hour. In the old channel, the schools have dried out although some eater still flows in the deep channel toward the "Great Hell". The new channel cuts rapidly down through the loose sediments at the same time as it widens and shifts towards the north. (see the arrows on the profile.) The previously impressive waterfall changes quickly into a dead fall. we have a number of " dead falls" in Sweden these days. "Wild Hussen" was responsible in 1796 for creating one at Ragunda in Jämtland. During the e20th century many have been created by the hydroelectric projects. But here in Avesta we have the only dead fall in Northern Europe created by nature itself on a major river. Because of its short length of life, approx. 1 000 years, Avesta's oldest waterfall is still very steep, in particular the three "hells", which would have eroded much more if the water had been able to wear them down freely for some thousands of years. 6 000 years ago
B. Goat Ridge D. Badelunda esker (Ridge) C. Present level of river F. Sediment G. Moraine J. Boulder and pebbles I. Bedrock
4. Goat Ridge 7. Little Rapids 11. "Dead Falls no. 2"
The bedrock to the north of Goat Ridge, covered n rubble since the 1940's, slopes northwards which is why the new river channel eroded in that direction to its present position. The river eroded back through the loose sediments until it met solid rock at Little Rapids which, in its natural state, has a fall of 3 meters. At Great Rapids, 700 meters further upstream, there is another outcrop of solid rock and a more than 10 metre high cataract formed here, probably several thousand years ago. However, finally and probably at some time in the middle ages, the river cut a new channel north of the church through the present Great Rapids (see fig. 1). In the waterfall that was then made dry, Avesta's century which was, for a long period, the largest in the world. Power was provided by canals cut through the old river bed through to the dried out waterfall. Buildings were erected here with 4 rows of water‐wheels which powered hammers and bellows. During the 19th century, the cooper industry was gradually replaced by the iron industry. When the (older) Dead Falls had dried out, the river below them straightened out. The large bends where the golf course and hospital are now silted up and turned into two semi‐circular depressions. At extremely high spring floods, water still flows in the channel it occupied thousands of years ago.