PHOTOGRAPH BY MARKUS HELL, TAREOM.COM via AP
Published February 4, 2014
Two huge boulders sent tumbling by a landslide narrowly missed a farmhouse in Ronchi di Termeno in northern Italy on January 21, 2014. The above photo, taken two days later, shows one of the boulders after it rumbled down the hill and destroyed the barn before coming to rest in the vineyard—halted within a meter of the house.
The second boulder, hidden behind the house, stopped just short of the building. The boulder in the foreground is from an older landslide. Members of the Trebo family, who live on the farm, were reportedly unharmed.
Path of Destruction
These boulders appear to have originated from a large pillar of rock, probably limestone, says Ben Mackey, a geologist at the University of Canterbury in Christchurch, New Zealand. Erosion can cause pillars to slowly detach from the side of a cliff, then collapse, sending boulders tumbling down.
A Barn No More
It's unclear what triggered this rockfall, geologist Mackey says. But such rockfalls can be caused by storms or earthquakes. "Sometimes, though, rocks will fall with no apparent cause," he says. "Whatever was holding them in place just lets go. This makes predicting when rockfalls will occur quite difficult."
Falling Just Short
While smaller boulders tumble down cliffs often, Mackey says, huge rockfalls like this one are fairly rare. In a given location, boulders of this size would fall maybe once in many thousands of years. Mackey studies the old boulders of Christchurch to try and determine when they toppled over and how often such rockfalls may occur.
Falling Rocks Strike Twice
The fact that another boulder is nearby means that a similar rockfall happened in the past. Geologists usually use such evidence to decide how close to a cliff a building can be located and still be safe. "Generally, it would not be advisable to live under a cliff prone to rockfall like this," Mackey says.
Ok, so we'll put the house here, the barn there, and the vineyard there! I wonder where that boulder came from? hmmm.
One basic thing in storytelling is missing - at least one picture of the top of the hill. I could understand if this is story from the Sun or such magazine, but in National geographic? Shame... How can we imagine where those rocks came from? Nice reading, but pictures don't show us the whole story
For the curious, I'd estimate weight for the boulder that went the furthest to be about 600 tons plus or minus about 100 tons. That is based on an estimated 12 radius roughly sphere shaped. Limestone would weigh just a little over 160 pounds per cubic feet. It appears to have stopped due to the hardpacked lane or driveway that failed to displace as easily as the vineyard soil.
I am very grateful no one was hurt; but maybe they can build some kind of bulwark under the incline.
First Boulder : "Damn ! Missed ! Hey Junior ! Keep more to the left and floor the house !"
Second Boulder : "Aaah ! I am here Pop ! Hyuk ! Hyuk ! Hyuk !"
First Boulder : "What ? (Looks Back) You idiot ! I told you to keep left ! You missed too !"
Second Boulder : "Huh ! I just followed your track, Pop !"
First Builder : "Now another 1000 years before another rock gets a chance !"
Second Boulder : "Awww, shucks !!!"
This is an 'amazing' event no doubt. Here is a thought of mine on this; an invisible force has caused this to happen in this location. Certainly once and definitely twice. Gravity! Erosion from rain and the elements is at work, but gravity is what makes events like this occur!
Love the photos and it is the first time I have ever seen something like this.
I guess you could say that "Gravity Rocks!" :-)
Wow, this is something I would normally hardly agree to believe it happened. Amazing and curious event!
yes this is too close for comfort.
I will relocate myself;
because next time that happens you're probalby dead
The folks here must have had some warning this was going to happen: notice that the power line tower on the left side of the vineyard has been freshly bermed around with a guard to prevent rocks from taking the tower out.
Noting the comment about the "rarity" of this event, that could be easily determined by counting the large rocks on the slope. Such rocks would not readily disappear once they fall. There is probably community memory of such events also. Large rockfalls like this would not be unnoticed by those who have lived here over several generations. The rate of fall has probably not changed over hundreds of years and is driven by long-term processes rather than by current practices. Again I have to note that the detailed on-site examination should determine this.
Looking at the distant images again, I note that other houses are present in the danger zone. I anticipate that the governmental authority or at least a homeowners' group will have a geotechnical expert investigate this slide and the rest of the cliff to determine what practical response can be done to protect the lives of those living in the danger zone.
This interests me as a geotechnical engineer. I "Googled" the location to get more photos so I could see the upper part of the slope. The landslide appears to be limited to just a few large blocks that toppled from the cliff at the top of the hill, with other sliding material just being that knocked loose by the boulders as they tumbled downhill. This is part of the natural weathering and slope reduction process at work. It is hard to predict when this thing would happen, though close examination of the cliff might have identified the unstable blocks ahead of time by looking at the bounding cracks and height relative to block width, which determines block toppling stability.
Not much cheap can be done to stabilize such blocks. Since the farmhouse is a small target, the area of the cliff that poses a risk of future falls can be identified and a very careful examination may allow identification of the remaining unstable blocks. Then it may be possible to tie the blocks back with tensioned anchors drilled through the top of the blocks into the rock behind them, if this location can be accessed to allow this. A relatively moderate horizontal force applied to the top of such blocks through such anchors would probably stabilize them. I say this based only on the distant picture that gives me the impression that the ground below the blocks does not appear to have failed on a large scale. They appear to have toppled on their own, which means they rotated outward from the top with limited crushing or other failure of the material below the toe of the blocks. This would of course have to be examined at the site to verify this guess. It would probably be worth at least evaluating the cliff to define this as the farmhouse appears to be historic and valuable. The alternative would be to abandon the house and move lower down the slope. Tying the relevant remaining blocks back as mentioned above is likely to be the least expensive of effective ways to protect the house. Stopping or deflecting such blocks once they start going would require a massive barrier that is likely to be more expensive than anchoring the blocks at the top of the slope (if this is practical). Again, this would have to be verified by a detailed examination of the slope and cliff (which is probably being done).
The instability of such blocks develops over a long period of time, but the triggering event that finally releases them could be an unusually wet year with lots of groundwater pressure, a minor earthquake, or any minor event that shakes or weakens the unstable block and its base. Eventually such blocks are going to fail and the longer they weather, the lesser the triggering force necessary to finally release them. The cause is the long-term deterioration of the block and its base by weathering, but the time when the forces driving it downward exceed those restraining it cannot be predicted as the events that act to trigger such a rock fall vary in effectiveness and the times they occur cannot be predicted.
Hopefully, no one was injured; this is a reminder of the forces constantly at work on our planet. How our lives can be change in an instant.
@Tony Cooley Here's an idea. MOVE THE HOUSE. If they can move London Bridge........
@HASSAN NAGAH There is no god. Move your propaganda elsewhere.
@HASSAN NAGAH So you're saying rock has an emotional response to your god? Only this rock, this random rock on a random hill. Lol. I'll stick to science on this one.
@HASSAN NAGAH Someone has far too much free time.
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