Glacial erratics are boulders carried from higher in the mountains and deposited on a surface of different material than the erratic. The power of ice to carry huge amounts of matierial is evident by the size of erratics - some are house-sized and weigh tons. This explains how giant boulders from miles away high in the mountains come to rest in such odd places.
This large bolder is a glacial erratic
Geologists know this rock is different from the soft local sandstone. It is hard quartzite from the Rocky Mountains. If you look closely at the rock, as I did, you can see layers of sand with small amounts of silt and pebbles. These layers of sediment were deposited between 570 and 540 million years ago in a shallow sea, long before the uplift of the Rocky Mountains. Gradually, the sand layers were buried under hundreds of feet of sediment which generated considerable heat and pressure. Under these conditions the sand grains were compressed and cemented into an extremely tough, durable rock known as quartzite.
During the formation of the Rocky Mountains between 150 and 50 million years ago, these quartzite beds were thrust upwards several thousand feet. Subsequent erosion has exposed these beds in the Main Ranges of the Rocky Mountains around Lake Louise, several hundred miles north of here.
Rockslides from the quartzite mountain peaks cascaded onto the surface of a passing valley glacier in the Jasper area. Geologists generally believe that this took place about 18 thousand years ago. The glacier then transported the quartzite blocks out onto the plains to their present resting places. Cobbles from the quartzite beds of the Rocky Mountains are commonly found in gravel throughout Alberta. The hard quartzite cobbles were often flaked into stone tools by Indigenous peoples of the plains. The durability of the quartzite provided tough, long-lasting cutting edges for their knives and scrapers.
Large boulders, like this one, left by glaciers are known as glacial erratics. Over the past two million years during a time geologist call the Pleistocene Epoch, a series of glaciers moved across the Head-Smashed-In area of Alberta, Canada. Often these massive sheets of ice picked up and carried with them huge amounts of rock. The erratics near "Head-Smashed-In" are part of a "train" of these boulders scattered along the foothills extending from Jasper National Park to southern Montana. This train of boulders was deposited by glaciers probably sometime it the last 50,000 years.
Large split glacial erratic in open prairie in the Head Smashed-In area of Alberta, Canada
Many of the rocks that form the "Foothills Erratics Train" lie fractured in the prairie sun. What caused the quartzite to split? Geologist attribute this to natural processes.
Glacial Erratic in Yellowstone National Park
Not all geology in Yellowstone was created by volcanic activity. This is a large glacial erratic dropped here by a glacier thousands of years ago. This large boulder is of different material than the surrounding rocks. It was transported here by a glacier that melted thus releasing this "rock" here, far away from where it originated. It is 15-miles from its nearest place of origin. It was dropped from melting ice (the glacier) about 10,000 years ago.
By the way you can see this large (estimated to weigh 500-tons) "eratic" or "glacial boulder" on the road from Canyon Visitor Center to Inspiration Point in Yellowstone, National Park.
These large boulders are glacial erratics.
Far from their origins, these giant boulders were carried by ice for many miles before being abandoned and dropped by the melting glacier.
A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. These glacial erratics in the Lamar Valley of Yellowstone National Park are perect examples.
In geology, an erratic is material moved by geologic forces from
one location to another, usually by a glacier.
The large boulders are glacial erratics scattered in the Lamar Valley of Yellowstone National Park.
Glacial erratic in Sinks Canyon, Wyoming. It is granite, yet the walls of the canyon are sandstone and limestone. The nearest granite is 30-miles away high in the Wind River Range
Glacial erratics are boulders carried from higher in the mountains and deposited on a surface of different material than the erratic. The power of ice to carry huge amounts of matierial is evident by the size of erratics - some are house-sized and weigh tons. This explains how giant boulders from miles away high in the mountains come to rest on the sandstone and limestone floor of Sinks Canyon near Lander, Wyoming.
Glacial erratic near Lander, Wyoming
A long gone glacier dropped these erratics all over this meadow in the Wind River Range of Wyoming.
Erratics such as these can be easy to spot since they are always sitting where they should not be.
These were on Louis Lake Road out of Lander, Wyoming.
Mike & Joyce Hendrix
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