One analysis examined deformation in the Joshimath area between April and November 2022, showing about 9 cm of movement over the seven month period.\u00a0 This is the resulting diagram:-<\/p>\n
![\"ISRO](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/23_01-Joshimath-InSAR-1.jpg\")
ISRO InSAR map of deformation at Joshimath over a seven month period to November 2022.<\/em><\/p><\/div>\n .<\/p>\n The second analysis examined deformation between 27 December 2022 and 8 January 2023:-<\/p>\n ISRO InSAR map of deformation at Joshimath over the period from 27 December 2022 to 8 January 2023.<\/em><\/p><\/div>\n .<\/p>\n Now, I think it is important to put three caveats on this analysis.\u00a0 First, InSAR measures line of sight movement, not absolute deformation.\u00a0 Thus, to interpret the data properly it is essential to understand the line of sight but, with the document no longer available, this is not clear.\u00a0 Second, this is labelled as subsidence, but that is potentially misleading.\u00a0 The movement is clearly landslide movement, and so is likely to be parallel or subparallel to the slope (whereas subsidence might be interpreted as being vertical).\u00a0 Third, the magnitudes of deformation do not seem to conform to observations on the ground.\u00a0 Whilst not trivial, 5.4 cm of movement is insufficiently large to cause the damage seen.\u00a0 Images such as the one below suggest deformation that is much greater than this:-<\/p>\n A tension crack at Joshimath. Image by The News Himachal<\/a>.<\/em><\/p><\/div>\n .<\/p>\n I am unsure as to the cause of this anomaly – it could be the line of sight issue noted above, or the consequence of an initial analysis, or maybe the largest deformations occurred before 27 December.<\/p>\n However, the analyses provide key information.\u00a0 This appears to be a conventional landslide, almost certainly a reactivation of a part of the existing relict failure.\u00a0 The landslide is affecting the main part of the town, and extends close to the toe of the slope (the InSAR data may be unreliable in the very steep sections of slope close to the river).\u00a0 This might indicate that an element of the issue is toe erosion, raising the intriguing prospect that the Chamoli debris flow<\/a> might have played a role.\u00a0 Some of the worst affected buildings, such as the two hotels that are being demolished, appear to be in the area of the lateral scarps.\u00a0 This is common.<\/p>\n The fact that the landslide is affecting the town and not the surrounding areas might hint that local factors\u00a0 – slope cutting, poor water management, inadequate engineering – could be playing a key role in the instability.<\/p>\n Of course the most important implication is that many properties at Joshimath are at risk.\u00a0 There are reports that the problem is continuing to get worse<\/a>, with 723 buildings now considered to be unsafe.<\/p>\n Finally, there is a very interesting proposed paper on the NHESS website<\/a> (Sundriyal et al.<\/em>, for comment 2023<\/a>), submitted in late December, that considers the problems at Joshimath.\u00a0 \u00a0This paper is open for comments.\u00a0 The paper highlights the state of instability and indicates that large amounts of deformation (in the order of metres) are possible.\u00a0 If this were to occur then a very large number of buildings in the town will be lost.<\/p>\n .<\/p>\n![\"ISRO](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/23_01-Joshimath-InSAR-2.jpg\")
![\"A](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2023\/01\/23_01-Joshimath-crack.jpg\"){kind=spacer}
Reference<\/strong><\/h4>\n