October 6, 2016 at 4:27 pm

The Great Bonneville Flood – Part 2

by
PDF pageEmail pagePrint page

 
 
In Part 1 of this account I discussed a gigantic ice age lake called Lake Bonneville, and its catastrophic overflowing. I described this vast body of water and hoped to impart a sense to the reader of its immensity, it having once covered well over 20 thousand square miles of modern day Utah and parts of southern Idaho. This is quite remarkable in its own right but what is really interesting is what happened when the lake reached its maximum extent near the end of the last ice age and began to spill over a mountain pass on its northern rim. That pass is now known as Red Rock Pass, also Red Rock Junction, due to the color of its exposed sedimentary rocks. It lays in southern Idaho about 25 miles north of the Utah-Idaho state line. U.S. Highway 91 now runs north-south through the pass. Anyone driving that route will be crossing through the breakout spillway of the Great Bonneville Flood.

Figure 4. Red Rock Pass – the outlet for the great Bonneville Flood. The town of Zenda sits right in the spillway carved by the draining floodwaters. Flow was towards the north, following the pathway now occupied by Highway 91.

Figure 4. Red Rock Pass – the outlet for the great Bonneville Flood. The town of Zenda sits right in the spillway carved by the draining floodwaters. Flow was towards the north, following the pathway now occupied by Highway 91.

Sometime between about 13 and 15 thousand years ago the northernmost arm of massive Lake Bonneville stood against a dam of relatively soft sedimentary rock and alluvium that blocked Red Rock Pass. As Lake Bonneville deepened rapidly at the end of the last ice age the water rose some 400 feet against this unconsolidated rock. At some point, as the planet began its lurch out of the ice age vast Lake Bonneville spilled over this dam. As the waters poured through the mountain pass they quickly ate their way through the 400 feet of softer material until they excavated down to a harder layer of granitic rock and there the lake stabilized for a time.

red rock pass, eroded, remnant, flood outburst, randall carlson

Figure 6. An eroded remnant of the sedimentary rocks in Red Rock Pass. Note the reddish color. Before the flood outburst the floor of the pass was at least at the level of the top of this eroded knob. The gravelly material banked up against the knob was deposited as wash by the declining flood currents. Photo by Randall

Between the time of the initial spillover and the point at which the flood terminated upon reaching the harder rock, about 1000 cubic miles of water poured through the breach. If you choose to you may look at a map of Idaho and note where U.S. 91 converges upon Interstate 15 about 15 miles north of Red Rock Pass. From here Interstate 15 follows the route of the flood north through Marsh Valley and then along the Portneuf River Valley until it reaches the town of Pocatello, Idaho.

Pocatello Idaho, Great Flood, Snake River Plain, Randall Carlson

Figure 7. Pocatello, Idaho. The great flood route followed the blue arrow, discharging out onto the Snake River Plain at the site of modern day Pocatello. View looking east from roughly 15,000 feet. Photo by Randall

At Pocatello the Portneuf Valley opens out onto the Snake River Plain. (See my essay about the Teton Dam disaster) From here the flood flowed into a preexisting natural lake that occupied the basin now containing American Falls Reservoir. This lake was both fed by and drained by the pre-flood Snake River. As the massive gush of water followed this already existing route it gouged out about 400 feet of bedrock, cutting a canyon with shear basalt walls that was over a mile wide in places.

Perrine Bridge, Snake River Canyon, Gorge, Bonneville Flood, Randall Carlson

Figure 8. Perrine Bridge over Snake River Canyon. This 400 foot deep gorge was largely created by the passage of the Great Bonneville Flood, peaking at about 40 million cubic feet per second. Photo by Randall

The Great Bonneville Flood was an exceptionally powerful flood. The first geologist to study this colossal fluvial event was Harald Malde with the U. S. Geological Survey. In his U.S.G.S. Professional Paper published in 1968 he stated:

“The enormous size of depositional and erosional features produced by the Bonneville Flood imply a peak discharge of extraordinary volume.”

The ancient channel dwarfs the channel of the modern river. This situation depicted here is called by geologists an underfit river, in which the present day stream or river is disproportionately small when compared to the channel in which it is flowing.

Other geologists who have studied the Bonneville Flood compared its power to that of several modern floods that occurred on the Mississippi and Amazon Rivers. These floods, which are large and powerful by modern standards were trifling when compared to the power of the ancient Bonneville Flood. In terms of Newtons, the unit of force used by both geologists and physicists, the modern day Mississippi and Amazon floods exerted about 12 Newtons of force, whereas the mighty Bonneville Flood exerted about 75,000 Newtons, or about 6,250 times more stream power than the large modern floods! This is an almost inconceivable power. The thrust generated by an F100 fighter jet is about 130,000 Newtons, or only about 1.7 times greater than that of the Bonneville Flood. So to help the reader to come to terms with what kind of force I am talking about some pictures will be invaluable. In this first photo we see the canyon cut by the flood in which the modern Snake River flows. The ancient channel dwarfs the channel of the modern river. This situation depicted here is called by geologists an underfit river, in which the present day stream or river is disproportionately small when compared to the channel in which it is flowing.

scale invariance, geology, bonneville flood, snake river, ancient channel, randall carlson


Figure 9. A beautiful example of scale invariance in geology. The diminutive modern Snake River is flowing within the giant ancient channel left behind by the mighty Bonneville Flood. View looking east from roughly 2500 feet altitude. Photo by Randall

The present day Snake River as seen in this photo has an average annual discharge of about 57,000 cubic feet per second. The ancient Bonneville Flood River that cut the large channel was about 600 times greater in volume. So powerful was the current that the sediment load it picked up and swept along can hardly be called sediment. Try to imagine the power of the current flow that could pick up and transport the two boulders in the next photo. These enormous rocks were deposited about 10 miles below American Falls Reservoir.

Massive, Boulders, Flood, Transported, Great, Bonneville Flood, Randall Carlson


Figure 10. Two massive flood transported boulders testify to the almost inconceivable power of the Great Bonneville Flood currents. Photo by Randall.

horseshoe cataract, Shoshone falls, basalt bedrock, flood,


Figure 11. Huge horseshoe shaped cataract over which a mighty waterfall once poured. Modern day Shoshone Falls is miniature by comparison. At the peak of the flood passage the entire landscape in this scene was submerged under a roaring, violent torrent of water. The tortured texture of the basalt bedrock testifies to the power of this flood.

snake river, canyon, twin falls, erosional forms, extinct cataracts, canyon

Figure 13. In this Google Earth image one can see the Snake River as the blue line following the canyon. The large brown and barren area was a flood path, etched into the landscape as the waters overwhelmed the canyon and flowed overland, eventually rejoining the canyon here, in the region of Twin Falls. Note the erosional forms and extinct cataracts where the huge sheet flood rejoined the canyon.

About 200 miles further west the power of the flood was still enormous. In the next photo the author is seen standing on the giant Swan Falls boulder bar left in the wake of the flood. This bar is nearly 3 miles long and is composed of uncountable thousands of giant flood rolled boulders. The boulder bar lies the floor of the Snake River canyon, whose northerly wall can be seen in the background rising nearly 700 feet above the modern river.

Giant boulders, flood, bedload, brad young

Figure 14. In the field of giants. Massive flood currents cut the canyon in which the author is standing and then deposited a giant bar of boulders that were being carried as bedload sediment. Thankfully, the world has been spared events of such power and magnitude in recent times. Photo by Brad Young

To the west of Swan Falls the great currents turned north and contributed to making Hell’s Canyon the deepest in North America. At Lewiston, Idaho the flood turned west and coursed over southeastern Washington State until it joined up with the Columbia River, ultimately making its way to the Pacific Ocean. The effects imprinted into the landscape of southern Idaho testify to the occurrence of a natural event of inconceivable power and scale. But, it is at Lewiston that something truly astounding happened. Here the waters of the Bonneville Flood met those of the Great Missoula Flood, a monstrous fluvial event that exceeded in size and scope that of the Bonneville Flood by more than a full order of magnitude. I will have more to say about that event.

The effects of such powerful floods can only be appreciated when they are experienced firsthand in the field. If a picture is worth a thousand words the real thing is worth a thousand pictures. But, as impressive as it was, the Great Bonneville Flood was only a part of a much larger event that involved the entire planet, literally bringing one world age to an end and inaugurating a new planetary order that still prevails today. For 12 millennia this story has waited to be told. For 12 millennia the vast scale of the events during this time of extreme planetary transformation and renovation has precluded perception, recognition and comprehension by humankind. Only within the past few decades has our discernment evolved to a level capable of perceiving what lies simultaneously concealed and revealed in the world all around us.

But, as impressive as it was, the Great Bonneville Flood was only a part of a much larger event that involved the entire planet, literally bringing one world age to an end and inaugurating a new planetary order that still prevails today. For 12 millennia this story has waited to be told. For 12 millennia the vast scale of the events during this time of extreme planetary transformation and renovation has precluded perception, recognition and comprehension by humankind.

It is nothing less than the wreckage of a former world, a world destroyed and wiped away in the aftermath of an intense period of planetary convulsion. It is out of this wreckage that we have, literally, constructed our modern world. It is the vastness of the phenomenon that has rendered it for so long invisible and unrecognized to the human eye.

Until now.

For all those who are paying attention, whose eyes and minds are open: the veil is parting and the deep history, the real history of humankind on planet Earth is emerging from the mists and shadows of antiquity. The Great Mystery has bided its’ time for a World Age, while the hands of the celestial clock have marked the passage of the cosmic hours and the Equinoctial pointer begins its’ passage into the 11th hour.
The time of revelation is nigh at hand.

Will it confer oblivion or exaltation? The choice is ours.

– Randall Carlson

Support SGI!

 

Donate $5.55/month
Donate $7.77/month
Donate $11.11/month
Donate Any Amount

 

gnosis-sale-poster

  • Bethany Brandon

    Thanks again for an excellent piece. You manage to make these astounding events seem so “real-time” — the Snake River photo is an example: getting that perspective is like suddenly opening my eyes and really SEEING what happened, seeing it HAPPENING, in fact. With your wonderful detailed descriptions to explain what I’m looking at, it’s just breathtaking-! I wish everyone got as excited about the geology of our landscapes… Keep going, Randall!