Mysterious Moving Boulders Are Lifted By Storms

[emerald]

"For years, geologists have puzzled over mysterious boulders that litter the desolate coastline of Ireland's Aran Islands. When nobody is looking, the massive rocks somehow move on their own.

What unseen hand is capable of ripping a multitude of heavy boulders from the craggy cliffs below and tossing them so far inland?

While some researchers contend that only a tsunami could push these stones, new research in The Journal of Geology finds that plain old ocean waves, with the help of some strong storms, did the job. And the waves are still at it.

The sizes of the boulders in the formations range "from merely impressive to mind-bogglingly stupendous," writes geoscientist Rónadh Cox, who led the research with her students from Massachusetts' Williams College

One block the team studied weighs an estimated 78 tons, yet was still cut free from its position 36 feet (10 meters) above sea level and shoved farther inland.

The team used two methods to nail down waves as the culprit. They compared modern high-altitude photos of the coastline to a set of meticulous maps from 1839 that identified the location of the boulders' ridges — nearly 100 years after the most recent tsunami to hit the region, which struck in 1755.

The comparison revealed that boulders moved inland over the years, some at an average rate of nearly 10 feet (3 meters) per decade.

In addition, the team used radiocarbon dating to pinpoint the time when tiny clams secreted in the boulders' cracks were removed from the ocean, a parameter that indicates when waves tossed the peculiar rocks on land. Some appeared in the last 60 years.

"There's a tendency to attribute the movement of large objects to tsunami," Cox said. "We're saying hold the phone. Big boulders are getting moved by storm waves."

http://news.yahoo.com/mysterious-mov...163408751.html

[size_of_light]

The team used two methods to nail down waves as the culprit. They compared modern high-altitude photos of the coastline to a set of meticulous maps from 1839 that identified the location of the boulders' ridges — nearly 100 years after the most recent tsunami to hit the region, which struck in 1755.

The comparison revealed that boulders moved inland over the years, some at an average rate of nearly 10 feet (3 meters) per decade.

Not sure how comparing a modern day high-altitude map with a map from 1839 could tell you that they moved 10 feet per decade.

That should only reveal that the boulders were at point A in 1839 and are at point B now.

In addition, the team used radiocarbon dating to pinpoint the time when tiny clams secreted in the boulders' cracks were removed from the ocean, a parameter that indicates when waves tossed the peculiar rocks on land. Some appeared in the last 60 years.

Again, that should only indicate that those boulders were tossed on land 60 years ago, not that it was a gradual process created by storm waves.

There might be hard science that enabled them to reach these conclusions, but the yahoo article doesn't go into it.

Hopefully these scientists know what they're talking about...

The sizes of the boulders in the formations range "from merely impressive to mind-bogglingly stupendous," writes geoscientist Rónadh Cox, who led the research with her students from Massachusetts' Williams College

Such a very scientific term.

Maybe this is all boulder-dash (nyuk-nyuk!).

[moving finger]

She's just speaking to a less educated audiience.

This is the Journal of Geology article the yahoo page is reporting:

http://www.jstor.org/discover/10.108...id=56148457503

Ireland’s Aran Islands are an excellent place to test whether coastal boulder deposits—including individual rocks weighing several tens of tonnes near sea level and clasts weighing several tonnes transported at tens of meters above sea level—require a tsunami for emplacement or whether storm waves can do this work. Elongate deposits of cobbles, boulders, and megagravel are strung along the Atlantic coasts of the Aran Islands. No tsunamis have affected this region in recent centuries, so if these deposits are forming or migrating at the present time, they must be storm activated. We find a diverse range of evidence for recent ridge activity. First, shells of Hiatella arctica (subtidal rock-boring bivalves preserved in life position within ridge boulders) yield radiocarbon ages from ≈200 AD to modern (post-1950 AD). Second, recent motion is attested to by eyewitness accounts that pin the movement of several individual 40–80-t blocks to a specific 1991 storm and by repeat photography over the last few field seasons (2006–2011) that captures the movement of boulders (masses up to ≈10.5 t) even in years without exceptionally large storms. Finally, geographic information system comparison of nineteenth-century Ordnance Survey maps with twenty-first-century orthophotos shows that in several areas the boulder ridges have advanced tens of meters inland since the mid-nineteenth century, overrunning old field walls. These advancing ridges contain boulders with masses up to 78 t at 11 m above high-water mark, so wave energies sufficient to transport those blocks must have occurred since the 1839 survey. Thus, there is abundant evidence for ridge activity since the 1839 mapping, and as there have been no tsunamis in the northeastern Atlantic during that time period, we conclude that the Aran Islands boulder ridges are built and moved by storm waves.

It's available in full here:

http://madmonster.williams.edu/Paper...2012_JGeol.pdf

The language is a little more scientific

I've quickly skimmed through it and can't see those average figures quoted, so it may just be a bit of yahoo dumbing down, but it isn't unusual to reduce overall values to time specific ones. I have been involved in research into long term sediment yields and that's how it was done: you have a start point and an end point, you work out how much sediment has arrived and you average it out over time. It puts studies looking at erosion over decades on an equal footing with those looking over centuries.

It's actually an interesting piece of research they've done - combines anecdotal reports, historical sources and modern data collection techniques to produce a coherent overall story.

[don coyote]

This is a small boulder that sits in Grand Traverse Bay in Acme Michigan. You'll notice that it appears to have moved several yards by an unforseen means of locomotion.

It took me a while, but I discovered how it made it's way into shallow water on it's own.


..... Can YOU determine how it got there?

[don coyote]

.....And yes,... this is the town where my Cousin "Wyle E." would buy all his hardware supplies.

[moving finger]

Originally Posted by don coyote

This is a small boulder that sits in Grand Traverse Bay in Acme Michigan. You'll notice that it appears to have moved several yards by an unforseen means of locomotion.

It took me a while, but I discovered how it made it's way into shallow water on it's own.


..... Can YOU determine how it got there?

Unless the answer is "the water level changed" I don't know. Put me out of my misery lol!

[sartori]

Interesting OP Emerald, with a good followup by Moving Finger and a straight up quality pun by Size of Light!

[don coyote]

Okay,..... I've given you a few days, and no-one cares, so here's the answer.


This particular rock used to sit about 30-50 yards out in the bay. There was only a few inches of it sticking up out of the water and seagulls would stand on it. (My Wife named it "Seagull Rock" ).

So during the winter, the ice had encased the rock far enough to secure it in place within the ice. Throughout the winter, the lake levels drop due to the buildup of the ice. The ice floats upon the lake-surface and grows thicker from the top down, building up more ice around the rock. As the ice melts in the springtime, it melts from the middle of the lake inward, and the lake water levels rise again which floats the ice up higher than it had throughout the winter... and that little boulder, having been secured in place within the ice, got picked up off the lake bottom far enough to move into shore with the sheet of ice as it melted. The higher the lake levels became, the farther into shore the wind would blow the drifting sheet of ice. (Half-anchored by the rock). It left a trail in the mud to mark it's distance travelled which still exists after a year-and-a-half after it's journey.

I took that picture last Fall after the rock had been moved earlier in the spring of 2011.
(The water level was higher in the spring, they typically drop throughout the summer,... which is why there is not much water under the rock when this picture was taken).



These boulders in Ireland (and elsewhere) could be being moved by ice. If ice builds up dramatically during low tide, then the boulders may be floating around at will at high tide.




(Or Aliens may be moving them around and inspecting them for use in landscaping their yards, back on their home-worlds).