Fusa's Finest #4: Jettergrytene EarthCache

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Hidden : 9/11/2010
Difficulty:
2.5 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


The Giants Kettles in Fusa: Get boiled!


10/10/10: Earth Cache Day!




This cache is a part of the series "Fusa's Finest":
Den Store Steinen (GC27CPQ)
Horgaberget(GC27TDE)
Fusafjellet (GC27TFG)
Havsgårdsvatnet (GC28PGT)
Bygdastølen (GC2F1RR)



Welcome to Fusa; the municipality of The Three Giants Kettles.

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ABOUT THE FUSA GIANTS KETTLES:

This cache is located in Eikelandsosen, by / in the river just above the Koldal waterfall. There are two neighbouring Giants kettles just next to the river. There are several Giants kettles in the municipality of Fusa. The last one is located "downtown" Eikelandsosen and is also a part of this earth cache. You will find the coordinates to this pothole as a waypoint, below.

The two neighbouring Giants kettles by the Koldal river are among the biggest in Norway. The third one is not a tiny cooking pan either.

Fusa has made these three Giants kettles their trade mark, and You will find them in Fusa's coat of arms, illustrated as three spirals. The word "Fusa" also means to flow powerfully, something which also inspired the choice of the design.
The coat of arms, designed by Arvid Sveen, was approved by the Royal resolution the 27th of September 1991.




Fusa's coat of arms.



THE FORMATION OF A GIANTS KETTLE:

In order to prevent confusion; let's clear the terminology: The terms "Giants kettle", "giants cauldron" and "pothole" are used to describe the same geological phenomena. To describe this phenomena in a river, the word "pothole" is often used.
You can read more about the origin of the words below.

 A Giants kettle or a pothole is a hole or a pit in solid rock which appears to have been drilled out, and where the surfaces seem to have been polished (by a fair amount of sandpaper).
This phenomena can be made in at least two different ways; in regular rivers and underneath a glacier where the glaciofluvial provides the neccecary energy.
What is common in the creation of all Giants kettles, however, is: water, stones/pebbles/gravel and not least a long period of time.

Most Giants kettles occure in shields; areas of igneous and high-grade metamorpic rock, which form tectonically stable areas. In all cases, the rocks are no less than 530 million years old, and can be as old as 3.5 billion years old. This means that the holes can be drilled over a period of millions of years.
When there are ancient rocks (granite, gneiss) with different resistance to erosion, strong pebbles sometimes fall in a small cavity with lower resistance to erosion than the surrounding rock. Flowing water makes this cavity wider and deeper. A Giants kettle is being made!

Hardness of pebbles must be the same or higher than the bottom of stream where the kettle is forming. In areas where there are diamonds and quartz rocks, you can actually still find the digging rock remaining trapped in the bottom of the pothole.
So if you want to go diamond hunting, look for a pothole. Diamonds are the hardest rock on Earth. Thoese hard rocks can eventually drill a hole in the side of the Giants kettle and escape, if the rock on the side is softer than the rock on the bottom.


River potholes
are made by eddying currents of water bearing stones, gravel and other detrital matter.
Pebbles and strong rocks are caught in a vortex of the river, some of which are visible in the image below.

This picture shows the Bourke's Luck Potholes in the Blyde River Canyon of South Africa .


Glacier Giants kettles
are made under a glacier; where the glaciofluvial has made vortices.
Water, produced by the thawing of the ice and snow, forms streams on the surface of the glacier, which, having gathered into their courses a certain amount of morainic debris, are finally cast down a crevasse as a swirling cascade or moulin. The sides of the crevasse are abraded, and a vertical shaft is formed in the ice.
The erosion may be continued into the bed of the glacier; and, the ice having left the district, the giants kettle so formed is seen as an empty shaft, or as a pipe filled with gravel, sand or boulders.
Such cavities and pipes afford valuable evidence as to the former extent of glaciers.

In rare occations, the glacier itself will be a part of the Giants kettle; where the pit is formed in the transition between the edge of the glacier and a cliff.¨The glacier will supply this spot with new ice for a long period of time, while the rock will erode.
When the glacier later disappears, only half a pothole will be left. When you see a half Giants kettles, this may be how it was made.
Another theory is that the rest of the Giants kettle has slid out later. Maybe the surfaces can give you a clue as to what has happened?


This picture is taken from "Vetlahelvete" Little Hell) in Aurlandsdalen in the west of Norway.


Wave made Giants kettles
Geologists also believe that potholes on the coastline may be formed by strong rocks and pebbles caught in a small pit, powered by waves to drill themselves further and further downwards.
This picture shows the Giants kettle at Sild, outside Lyngør in the south of Norway..


To sum up: The result is either:
- a closed Giants kettle, where the pebbles never escaped and are still there or has vapourized/eroded.
- an open Giants kettle, where half the pot was made out of ice from a glacier or has fell out.
- a semi-open Giants kettle, where the pebbles finally escaped out from the bottom of the pothole.



ETYMOLOGY:

The word "Giants kettle" refers to the size and the shape of this phenomena.
Earlier people thought that big boulders on a flat field had to mean that a troll or a giant had thrown them down from the mountains. They are often called Troll Stones. In the same way they thought that the Giants kettles were... excactly that: The Kettle or the cooking pan of a giant or a troll.
There has always been a lot of mystery and fear associated with the Giants kettles, and I imagine that they were, as so many other old superstitions, used to scare children from wandering off into the woods.

The name "Giants kettle" actually origins from Scandinavia.
The Swedish name "Jättegryte" means the same as the English word "Giant's kettle"; the cooking pan of a troll or a giant.
The prefix "jätte" means "very", thus the word "jättebra" means very good.
The Norwegian word "Jettegryte" is of course derived from the Swedish, and a Jette in Norwegian is a giant here as well. The Norwegian prefix for "very" is kjempe, and also means a giant. Thus "very big" in Norwegian is written kjempestor... which is exactly what a giant and its kettle are...


The Norwegian fairytale about Oskeladden (Ash lad) tells the story about a poor boy
who meets a hungry troll and saves his skin by challenging the troll in an eating bet.
The boy tricks the troll into believing that he can eat all he wants
by cutting a hole in his belly, when all he does is to cut a hole in his backpack.
The troll falls for the trick and kills himself.
Trolls are stupid! I guess this picture shows a real Giant's kettle...



TO LOG THIS CACHE:

Read the description carefully; your answers on nr. 2 and 4 should match the information in the cache description above.

1. First of all, I would appreciate if you took a picture of yourself OR your GPSr with the Giants kettle in the background and included the picture in your log entry. This is optional!
2. Study the two large neighbouring potholes. How do you think they were made? Why do you think that? (Read description above.) Send me a PM or an e-mail of your answer.
3. Some 20 meters upstreams you will find two small potholes; one in the river itself and one tiny on the riverside (See waypoint below). Include the approximated diameter of the smallest pothole in your PM / e-mail.
Note: If the water levels are very high, you won't be able to see the smallest one.
4. Go the the location of the third Giants kettle (See waypoint coordinates below). What type of a Giants kettle is this? (Read description above.)Include your answer in your PM / e-mail.


When you have logged the cache with the picture and mailed the anwers to me, you will recieve the Fusa's Finest code #4 :)
I will place 7 caches in addition to a bonuscache in Fusa during summer/fall 2010.






The most exciting way to learn about the Earth and its processes is to get into the outdoors and experience it first-hand. Visiting an Earthcache is a great outdoor activity the whole family can enjoy. An Earthcache is a special place that people can visit to learn about a unique geoscience feature or aspect of our Earth. Earthcaches include a set of educational notes and the details about where to find the location (latitude and longitude). Visitors to Earthcaches can see how our planet has been shaped by geological processes, how we manage the resources and how scientists gather evidence to learn about the Earth. To find out more click HERE

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