19 June 2018
Mars: a landslide triggered by a small meteoroid impact
The University of Arizona has released a really interesting image of the aftermath of a meteoroid impact on Mars that triggered a comparatively long run out landslide:-
The imagery was captured by the HiRISE instrument. The impact event is thought to have occurred about a decade ago. The meteoroid has created a crater with a diameter of about 5 m, and a more substantial impact debris field. The landslide appears to have initiated very close to the crater, but the crater itself remains intact:-
There is a good write-up of this in Universe Today:
In that time, the MRO has acted as a relay for other missions to send information back to Earth and provided a wealth of information of its own on the Red Planet. Most recently, it captured an image of an impact crater that caused a landslide, which left a long, dark streak along the crater wall. Such streaks are created when dry dust collapses down the edge of a Martian hill, leaving behind dark swaths.
In this respect, these avalanches are not unlike Recurring Slope Lineae (RSL), where seasonal dark streaks appear along slopes during warmer days on Mars. These are believed to be caused by either salt water flows or dry dust grains falling naturally. In this case, however, the dry dust on the slope was destabilized by the meteor’s impact, which exposed darker material beneath.
The impact that created the crater is believed to have happened about ten years ago. And while the crater itself (shown above) is only 5 meters (16.4 feet) across, the streak it resulted in is 1 kilometer (0.62 mi) long! The image also captured the faded scar of an old avalanche, which is visible to the side of the new dark streak.
In terms of morphology, this landslide is reminiscent of the rock avalanches flowing across ice, such as this example from Alaska:
It even has the distinctive digitate lobe structure seen at the toe of the landslide. The wonderful Mount Dixon rock avalanche video suggested that this structure can be formed by slow creep at the end of the main movement period.
18 June 2018
Hidroituango: a substantial step towards reducing the immediate risk
On Sunday a significant milestone was reached in the ongoing efforts to reduce the risks at the Hidroituango dam site in Colombia. Efforts have been ongoing to raise the crest of the dam, reducing the likelihood of it being overtopped by a wave triggered by the failure of the slopes around the lake. The first target was to reach 410 m, at which point the spillway became operational (should it be required). Yesterday the crest of the dam reached 415 m, providing considerable additional security.
The next target is 418 metres; the ultimate aim is to reach 435 metres.
The consequence of these improvements to the structure is that the level of warning has been reduced for a substantial part of the population living downstream from the dam. This improved dam safety, plus the decease of inflows as the mountains upstream from the dam move out of the rainy season, has allowed 11,000 people to move back. However, 4,000 people remain evacuated.
The image above shows he current state of the dam at Hidroituango. Note the very large volume of material tipped on the upstream face of the dam. This appears to be the material that is being used to try to reduce the leaks in the structure.
15 June 2018
Kilauea volcano: large-scale slumping on the rim of Halema‘uma‘u crater
The ongoing major eruptive event at Kilauea volcano in Hawaii has generated a wide range of spectacular videos and extensive news coverage. At the summit of Kilauea is the large Halema‘uma‘u crater, which has been undergoing major morphological changes in response to recent events. Most importantly, a little more than a month ago the lava lake that had occupied this space drained down. In response, the walls of the crater have undergone large-scale slumping. Volcanic landslides are well-documented, but rarely in this level of detail.
The USGS has a page that provides their latest photographs and videos of the Kilauea eruptive event, which includes remarkable imagery of these slumps. For example, this image shows the sequential curved tension cracks that mark the back of a series of large slumped blocks:-
Whilst the image below gives a wider perspective view of this slumping process. In some cases the slumped blocks have deformed by over 100 metres:-
There is a wonderful drone video, collected this week, that provides a panoramic overview of the deformation.
This is a textbook case of slumping in response to changes in the local stress state. We see successive slump blocks like this in conventional landslides too, though rarely with such clarity. A very interesting element of this is the lack of rotation in the blocks, none of which appear to be backtilted. I wonder if this is because of the circular planform of the blocks (whereas in non-volcanic landslides they tend to have a more linear planform). Presumably this circular shape inhibits the development of rotation.
The USGS have been monitoring the development of these slumps at Kilauea, so in due course there should be some fantastic data on the ways in which these landslides evolve.
14 June 2018
Rattlesnake Ridge: new drone footage of the development of the landslide
As expected by those responsible for monitoring the landslide, it has continued to creep over the last few months, and judging by the images it has now displaced by a few metres:-
Note the displacement of the tracks across the landslide, which give a good indication of the total movement of this part of the landslide. The slide has now formed a very clear head scarp (actually a double scarp, which is not unusual):-
The WADNR continue to monitor and manage the landslide, and they have a good website that provides details of their activities. I hope that in due course we will see a range of peer reviewed publications analysing the movement dataset that they are collecting.
12 June 2018
The Rohinghya refugees: landslides start to take lives as the monsoon arrives
For the last few months there has been increasing concern about the plight of many of the Rohingya refugees who have been forced out of Burma – Myanmar – by the military, and are now living in makeshift camps in Bangladesh. The numbers are vast – some estimates suggest over 700,000 people. There is particular concern about the camps at Kutupalong and the surrounding areas, which are thought to have a population that exceeds 500,000 people. The camps have been built on hilly, forested land that is highly susceptible to landslides. The trees have been felled to create space for the camps, and the makeshift accommodation has been built on and at foot of the slopes. Conditions are dire. CNN reports that Caroline Gluck, the spokesperson for the UNHCR, described the situation as:
“People are practically living on sandcastles”
The monsoon season has now arrived in Bangladesh. CNN also reports the first fatality of the rains (though not the first landslide fatality in the refugees camps this year):
“Around 2.30 a.m. Monday morning a mud wall in a shelter in the Kutupalong camp collapsed, killing a 3-year-old boy and injuring his mother”
Yesterday Nafeesa S tweeted a set of photographs of the conditions in the camps. For example, this image shows the weak state of the soil and the potential for collapse:
Whilst this image shows the houses built on deforested, weak slopes in the refugee camps:-
As of yesterday 21 landslides have been reported Over the next few days heavy rains are expected in Bangladesh. News reports this morning suggest that 13 people were killed by landslides overnight, although it is unclear as to whether these are refugees or the local population (who are also very vulnerable to landslides). The NASA TRMM model for landslide susceptibility highlights this area as being at risk at present:
The situation over the next few days is likely to be dire.
11 June 2018
Hidroituango – continued small landslides, and proposals for a way forward
The crisis at Hidroituango in Colombia grinds on, with the priority being to manage the situation through the remaining part of the wet season. The hope remains that as the rains cease the river flows will decline and the water level behind the dam will start to fall, reducing the groundwater level in the slopes and, hopefully, increasing the stability of the dam and surrounding slopes. To date the signs are that this approach is working. Meanwhile, large numbers of people remain displaced.
Meanwhile, small landslides continue to occur, and I assume the main slip is continuing to move. UNGRD (a national disaster management organisation, not a part of the United Nations) yesterday tweeted this image of the slopes above the abutment of the dam, which includes the unstable slope and the earlier landslides:-
This image is interesting in that it appears to show a series of new, shallow slips higher up the slope, some of which are not directly connected to the main slides. Presumably this is an indication of continued increases in groundwater level. One of these caused the evacuation of some workers on Sunday morning, although it seems to have been managed within agreed protocols. Note also how close the lake level is to the spillway. The water is now testing the rapidly emplaced fill at the crest of the dam; this is the material that has been reported to be below standard in terms of compaction.
Meanwhile a reader very kindly highlighted an article in the Medellin Herald that details possible solutions to the Hidroituango crisis, as outlined by the National Engineering Society of Colombia, SCI. There seems to be some frustration in the report that SCI did not have full details of the situation (“The SCI has not had access to the report presented by the North American commission of experts regarding [allegedly non-optimal material used for the emergency raising of the dam to 410 meters] standards, so we cannot endorse the [North American commission] recommendations not to plug the right diversion tunnel or not to close the water passage through the machine houses, which EPM should evaluate“), but it makes some recommendations along the lines that the problems will diminish when the water level falls, and that the situation can then be managed by slowly drying out the tunnels, building some new ones and fixing the damage.
However, this is quite an intriguing line in the report:-
“As for possible damage suffered in the cavern of the machine house, the special commission of the SCI was informed that according to the monitoring carried out, the cavern has not suffered any appreciable damage. Neither has there been detected any possibility of failure of the rock mass of the right massif [the mountain above the dam and machine house] and that all the underground [diversion tunnel blockage] events to date have been related to the location of the geological fault called Los Mellizos.
This appears to indicate that the landslide above the dam is superficial, which seems at odds with the images of deformation in the tunnels (which seem to be through the rock mass). The good news is that the damage to the infrastructure may be lower than had been feared, which might allow the project to be recovered in due course.
6 June 2018
Hidroituango: the potential for extremely large landslides?
The latest news from Hidroituango is that the movement of the landslide continues without major change. The Hidroituango twitter site posted a series of updates late on 5th June local time (early on 6th June UT) that indicate that:
1. In the last 24 hours, the behavior of the mountain on the right bank of the reservoir has been stable [I think this means stable sliding – i.e. no change in behaviour. It is certainly not stable from a slope stability perspective]. According to the data of the interferometric radar have presented some slides of surface material that reach Speeds less than 10 millimeters per hour, i.e. below the alarm threshold, which has allowed the continuous work of all the work fronts required in the project, except for the equipment that must advance work in the [plazoleta de compuertas = spillway?], due to the rain.
2. The two water leaks that have been detected in the dam wall are being kept under permanent observation. Both leaks, located in dimensions 375 and 375.3, do not record color or washing of fines and added its flow is less than 35 liters per second, so this Tuesday June 5 was progressed normally in the tasks programmed for its sealing by means of injections with bentonite, a clay that expands and improves the impermeability of the dam.
3. Water flows to the reservoir and downstream discharge are maintained at an average of 1200 m³/s. The reservoir level is 393.55 MASL, with an ascent rate of 0.4 meters per day
This information comes from the integrated information and alert Center, coordinated by EPM and operated 24 hours per day by specialized professionals, who adapt information obtained in real time and in a manner consistent with alerts notification protocols. For the PMU.
This situation was described yesterday as being “highly critical” by Jorge Londoño De la Cuesta, manager of EPM, yesterday.
The most interesting development though is a set of suggestions that the site could be affected by much larger landslides. For example, El Colombiano has a report online that appears to imply that an American report – presumably the report by the US Army Corps of Engineers? – indicated that the maximum volume of a landslide at the site could be between 10 and 40 million cubic metres. That would be an exceptionally large landslide – this is the realm of the high mobility (i.e. rapid) rock slide (although high mobility is not inevitable even at this volume), which could be very dangerous indeed. It isn’t at all clear to me how the topography shown below can generate landslides on this scale, but it is far from impossible. It would be very interesting to see this report.
Once again I am mindful of the extreme pressure on those individuals responsible for managing this crisis. The current situation must be extremely difficult to address, with so few options to gain control in the short term.
5 June 2018
Hidroituango – an increase in movement rate
In the last few hours, RCN Radio in Colombia has reported an increase in the movement rate in the landslide at the Hidroituango dam site, breaching the alarm threshold of 10 mm per hour. This has triggered evacuation of 45 workers at a part of the dam site. It is unclear as to whether this is merely the landslide showing typical stick-slip type behaviour, or a transition into a new phase of movement. Without a graph of the movement pattern this is impossible to ascertain. Meanwhile, the government is establishing a monitoring centre to collate the data, as recommended by the team from the United Nations and the US Army Corps of Engineers. This is a prudent move.
The same team has described a series of scenarios for the dam, as reported by BN Americas:
“They have established that we have a dam that is high risk, and that risk is associated with three main scenarios, some that are connected to the geotechnical risk of the mountainous mass or by landslide or damages to the powerhouse, which could trigger in the failure of the dam.
“The second scenario is that this unleashing would lead to a wave, as Minister Arce has just said, that will exceed the prey and also lead us to the failure of the dam.
“The third has to do with the dam itself: the top priority of level 385 to 410 and to 430, as has been established, can, by the way it was done to respond to the emergency, can generate some leaks and these filtrations could trigger in the failure of the dam, for which they recommend reinforcement of the priority filling, of the increase of the dam in these emergency conditions.
I think this means that they are concerned that: 1. Failure of the rockmass in the abutment (i.e. the landslide) could destroy the dam directly; 2. the landslide could trigger a wave that overtops the dam; and 3. the dam might fail because of seepage.
If so then this is a project is in deep, long term trouble. The lake level is currently rising at 70 cm per day, with the current level at 393 metres. The spillway is at 401 metres, so the lake level has to increase by another 8 metres yet. The groundwater will rise as the lake level comes up, with some lag, so the stability of the slopes will continue to decrease. Of course the lake level will increase beyond the spillway height in periods of heavy rainfall (there might be two metres depth of water flow through the spillway, unless the lake can be drawn down. If so then the lake level might top out about 10 m higher than at present, at some point.
Meanwhile, the two leaks at the foot of the dam are releasing 18 litres per second and 11 litres per second respectively. The authorities are trying to stem the leaks by sealing the site with bentonite. I remain unclear as to the source of water generating these flows.
Finally, a couple of weeks ago El Colombiano posted this video reportedly showing processes occurring within the tunnels at Hidroituango:
This was reportedly associated with the water flow in the machinery house. I have not seen anything like it – I am assuming that it was caused by cyclic pressure changes in the tunnel, driving condensation. I am not sure what this means, or why it was occurring. Does anyone have any insight?
4 June 2018
Hidroituango – continued slope movements and low volume seepage from the dam
In the last 24 hours there have been two interesting developments at the Hidroituango dam site in Colombia. First, more details have emerged of the incipient landslide that is causing considerable levels of concern. Lance Brown has kindly highlighted an article that provides details of the ongoing problems (caveated of course with the fact that this is a journalist’s interpretation of the technical details). The translation of the key parts of the Spanish text notes that:-
“The geological experts who monitor the right mountain of the Hidroituango project 24 hours a day, detected a 6 millimeters per hour detachment this Sunday, according to the report of the Unified Command Post (PMU) installed in Ituango, North of Antioquia. In this case no evacuation order was given to the workers who work in the dam and the landfill, because the alerts are lit when the movement is higher than 10 millimeters per hour, as happened in recent days.“
The implication is that the landslide is currently in a secondary creep phase, but 6 mm per hour is not trivial. Detailed monitoring should pick up any acceleration to failure, noting of course that failure is not inevitable. The article notes that the landslide was first detected on 29th May when:-
“Technicians of the UT company Grupo Líneas Suroccidente conducted an inspection in the mountain to know the conditions of two power transmission towers and after these works, it was known that there is a considerable risk scenario. This inspection, which was also done with EPM officials on Tuesday, May 29, resulted in a report known to RCN Radio, which argues that one of the towers could come down because “cracks are observed in the rock.” This authority held that these cracks, known as “saprolitos”, are characterized by the fact that the rock becomes a kind of putty, because of the humidity, and it foresees new landslides in the mountain.
Saprolitos – presumably saprolite – is chemically weathered rock, which is common in tropical areas and is known for instability problems. This of course raises questions as to the state of analysis of landslide hazard prior to construction of this project. These concerns are raised by another comment in the article:
“The most serious thing, according to this report, is that the “mountain also presents old traces of landslides of considerable size”, which shows that for some time there have been mass movements that have not been reported.”
I am not surprised if this is the case, but one wonders as to the degree to which these were mapped and analysed prior to the dam being constructed. And where are the other slides, and are they being monitored?
Interestingly, the article also includes this line:
“According to the photographs observed in the field and in a field visit, the geologist Osvaldo Ordóñez, professor at the School of Mines of the National University of Medellín, hired by the Government of Antioquia, indicated that it is necessary to carry out a controlled landslide to prevent the earth mass falls on top of the landfill and causes further damage.”
Be very careful! This is what was attempted at Vajont, with catastrophic consequences. It may be the right approach, but can only be undertaken under very, very carefully controlled circumstances, and the potential for a much bigger failure than expected cannot be excluded. Such an exercise should only be undertaken with very detailed preparation; I am not convinced that the current situation allows that.
But in another development, there is now evidence of water seeping from the base of the dam. There have been rumours that this is the case for some days now. Noticias Caracol has a video online that shows water emerging from the base of the dam, but notes that it is not considered likely that the source of the water is seepage through the dam itself.
The volumes of water are not large, so maybe this is dewatering of the dam material during the rapid emplacement to raise the crest (i.e. it is consolidation of the dam materials), or maybe it is seepage from the leaking tunnels. Either way this needs to be watched with care. Increases in volume would be an indication of greater concern.
I continue to feel that those managing the site are caught between a rock and a hard place. Ideally the water level should be drawn down, but the damage to the tunnels seems to make this impossible. The only way to control the lake level appears to be to use the spillway (and maybe this means that the tunnels can be repaired and brought back into use), but this means raising the water level, which in turn is destabilising the slope. This must be exceptionally stressful for all involved.
3 June 2018
The Hidroituango crisis: new landslides threaten the site
Over the last few days the Hidroituango crisis in Colombia has deepened considerably. El Pais reports (in Spanish that) the Colombian President, Juan Manuel Santos, stated yesterday that professional advice is that the level of risk has increased in recent days. The major problem is once again that of landslides, with new slope instabilities becoming evident as the level of the lake has risen. As noted previously, higher lake levels are generally associated with increased instability, and that appears to be the case here. The major issue appears to be a new landslide that has developed on the slopes above the dam. There are some good images of this problem on Twitter – for example, Mabel Gasca has tweeted this image of some of the tension cracks that have developed:-
Meanwhile, Diario Siglo XXI has tweeted this image of the site:
Whilst it might be hoped that this is a comparatively shallow slope failure, images from within the tunnels demonstrate that the cracks extend into the rock mass, unfortunately:-
Thus, the mass that is mobile is reported to have a volume of about 130,000 cubic metres. Whilst this is not a hazard on the scale of Vajont, there are two obvious threats. The first is that the landslide might induce a wave that overtops the dam, with potentially catastrophic consequences. The second is that the landslide blocks the spillway and intakes, meaning that the water levels can no longer be managed.
There is a little information about the specifics in this case, though news reports suggest that the authorities are getting advice from the UN and the US Army Corps of Engineers, which is good. The usual way to respond to this crisis would be to draw down the lake level (slowly) to increase stability in the slope, allowing time to develop a mitigation plan. However, in this case that may not be possible because the tunnels are blocked and unstable and, even worse, El Pais reports that rainy weather is on its way. This is a translation from the article:
On the other hand, the President said that starting next Wednesday there will be a tropical phenomenon in the area that will produce rain and possible landslides, but warned that they have nothing to do with the dam. For his part, the Minister of Mines and Energy, Germán Arce, said that the studies reached the conclusion that if the landslides continue, a wave could be generated that would put the area around the project at risk. “If a landslide occurs in a significant volume of material, this slip could generate a wave that exceeds the dam. That is, it returns us to that initial risk condition, “said Arce. A few hours ago Empresas Públicas de Medellín (EPM) had said that by next June 7, it was expected to reach the level of 415 meters above sea level in the construction of the dam so that the emergency risk could be reduced.
If the lake levels are going to rise, and the slopes are going to be wetted by rain in coming days, then the stability will likely decrease. This does not mean that a slope failure is inevitable, but it it is right to monitor closely and to evacuate those at risk. The Bogota Post reported yesterday that 25,000 people have been evacuated from downstream of the dam.
Many thanks to the various people who have sent info to me about the Hidroituango crisis, and in particular to Lance Brown, who has been tireless in his monitoring of this situation. You can see his various comments, with key links, at my earlier post. Apologies for my slow update – I was on leave in Singapore last week.