Geology.com has a spectacular sequence of images of a rockfall in progress in Yosemite National Park that are well worth a look. The images (which are explicitly copyrighted, so I have not reproduced them here) were collected by a well-known photographer, Herb Dunn, in the canyon of the Merced River.
The pictures show a fall from what appears to be a previously active rockfall scar. Below the scar there is a large area of rockfall debris. The falls appear to occur in granitic rocks, with the detachment being controlled by a series of large joints.
The failure in this case was apparently quite large - the bock was 30 m x 15 m - and appears to have come from a wedge failure at the top of the scar. As a result of the large fall height and substantial volume, the boulders have fragmented as they have impacted the slope, creating a spectacular plume of dust that rolls downwards. The rocks also disturb the accumulated and weathered scree that they hit, which means that the dust cloud starts to change colour in the third image as the discoloured material is kicked up. The fifth image captures some airborne blocks (see the bottom of the image in the centre), which are quite impressive.
Note that the failure has happened on a beautiful sunny day in August, so the trigger mechanism is not really obvious (thermal expansion maybe, or perhaps just progressive failure).
Showing posts with label 2006. Show all posts
Showing posts with label 2006. Show all posts
Monday, October 27, 2008
Friday, October 24, 2008
Forced to flee
IRIN, the UN Office for the Coordination of Human Affairs, has produced a rather nice video about the impact of lahars (a landslide in comparatively young volcanic materials) in the Philippines. The landslide occurred during Typhoon Durian (known in the Philippines as typhoon Reming) in 2006.
Wikipedia image of the track of typhoon Durian (Reming) in 2006. The orange dots indicate the locations at which the typhoon was at its maximum intensity
NASA image, derived from TRMM data, of the rainfall associated with typhoon Durian (Reming). Note that although 200 mm is very high, far greater rainfall totals are often associated with large typhoons.
Lahars surged down the flanks of Mount Mayon, killing over a thousand people. The film focuses on a comparatively affluent family whose house and land was hit by the lahar. The children's mother was killed, their house destroyed and their land inundated. In the aftermath the government declared the flanks of the volcano to be too hazardous, meaning that the family were moved into a refugee camp. The father of the family is relentlessly cheerful (except when he revisits his house and sees his wife's pillow), but his desperation is clear to see.
The film is available here.
Google Earth image of Mount Mayon, showing a lahar deposit. Click on the image for a full size view in a new window.
In many ways the most interesting aspect is the way that the film balances the hazards associated with the natural processes (i.e. the danger of another event) with the hazards associated with displaced people moving to new settlements that can quickly become slums. It is an interesting film that brings home some fundamental issues in a very real way, without presenting anything terribly new. It is certainly useful for teaching both in schools and at undergraduate level, and as a reminder to those of us working on hazards as to the complexity of the impact of decisions.
UNOSAT image of the impact of Typhoon Reming on Mount Mayon, showing in particular the multiple lahar tracks. Note the degree to which the lahars have impacted upon the towns.
Wikipedia image of the track of typhoon Durian (Reming) in 2006. The orange dots indicate the locations at which the typhoon was at its maximum intensity
NASA image, derived from TRMM data, of the rainfall associated with typhoon Durian (Reming). Note that although 200 mm is very high, far greater rainfall totals are often associated with large typhoons.Lahars surged down the flanks of Mount Mayon, killing over a thousand people. The film focuses on a comparatively affluent family whose house and land was hit by the lahar. The children's mother was killed, their house destroyed and their land inundated. In the aftermath the government declared the flanks of the volcano to be too hazardous, meaning that the family were moved into a refugee camp. The father of the family is relentlessly cheerful (except when he revisits his house and sees his wife's pillow), but his desperation is clear to see.
The film is available here.
Google Earth image of Mount Mayon, showing a lahar deposit. Click on the image for a full size view in a new window.In many ways the most interesting aspect is the way that the film balances the hazards associated with the natural processes (i.e. the danger of another event) with the hazards associated with displaced people moving to new settlements that can quickly become slums. It is an interesting film that brings home some fundamental issues in a very real way, without presenting anything terribly new. It is certainly useful for teaching both in schools and at undergraduate level, and as a reminder to those of us working on hazards as to the complexity of the impact of decisions.
UNOSAT image of the impact of Typhoon Reming on Mount Mayon, showing in particular the multiple lahar tracks. Note the degree to which the lahars have impacted upon the towns.
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