SAR Interferometric Point Target Analysis of Slope Instabilities in the Community of Biasca, Switzerland

Tazio Strozzi, Urs Wegmüller, Andreas Wiesmann and Charles Werner Gamma Remote Sensing, Gümligen, Switzerland

Lorenza Re and Giorgio Valenti Ufficio Cantonale Pericoli Naturali, Bellinzona, Switzerland

Hugo Raetzo Federal Office for Water and Geology, Biel/Bienne, Switzerland

Kaspar Graf GEOTEST, Zollikofen, Switzerland Community of Biasca, Switzerland Community of Biasca, Switzerland Community of Biasca, Switzerland Areas prone to deep landslides in northern Ticino

Content

Biasca - Loderio

Biasca - Fontana

Biasca - Canvasgia ERS SAR data between 1992 and 2000

66

32 Buzza di Biasca

Rockfall on September 30, 1513 from western side of Pizzo Magno

60 m high dam created after one year a 5 km long lake with about 200 Mio m3 of water

End, 1922 Buzza di Biasca

Lake outbrust on May 20, 1515 Stumpf, 1548 The terms buzza means in the local lombard dialect the material deposited by water after a natural catastroph Canvasgia _ + 23º from nadir

Mean displacement rate 1995-2000 ERS SAR data in descending -19 mm/year +1 mode Canvasgia

Valenti, 1998

sub-area 1 sub-area 2

Strozzi, 2004 Canvasgia

sub-area 2 Valenti, 1998 Canvasgia

-19 mm/year +1 Strozzi, 2005 Canvasgia Canvasgia 50 12

) 0 19 m m ( t p35498 n

e -50 m p35411 e c a l p -100 p35230 s i d

t 3-d displ. h g i

s -150 f

o 362 mm e n i (49 mm/y)

L -200 354 mm -250 (53 mm/y) 5 6 8 9 0 2 3 9 9 9 9 0 0 0 9 9 9 9 0 0 0 .1 .1 .1 .1 .2 .2 .2 4 8 1 5 0 2 6 .0 .0 .0 .0 .1 .0 .0 1 3 5 0 1 3 8 1 2 0 2 0 1 2 Community of Biasca, Switzerland Fontana (Val Pontirone) Areas prone to deep landslides in Ticino, I-II-III are saggings _ + 23º from II nadir

I Mean displacement III rate 1995-2000 ERS SAR data in descending -19 mm/year +1 mode Fontana (Val Pontirone) Molignani, 1996 Sagging I: Morpho- structural elements Fontana (Val Pontirone) _ + 23º from nadir

Mean displacement rate 1995- 2000 ERS SAR data in descending -19 mm/year +1 mode Fontana (Val Pontirone) _ + 23º from nadir

Mean displacement rate 1995- 2000 ERS SAR data in descending -19 mm/year +1 mode Fontana (Val Pontirone) Disposizione dei punti (Valeggia, 2001)

4 3

7 5 2 6 8

9 10 11 12 15 1 13 14

STAZIONE 100 Fontana (Val Pontirone) Fontana (Val Pontirone) Fontana (Val Pontirone)

0

-50 (mm)

-100

-150 displacement 11 -200 21305 LOS 21374 -250

31.01.1993 15.06.1994 28.10.1995 11.03.1997 24.07.1998 06.12.1999 19.04.2001 Fontana (Val Pontirone)

0

-50 (mm)

-100

-150

displacement 15 -200 12 LOS 21038 -250

31.01.1993 15.06.1994 28.10.1995 11.03.1997 24.07.1998 06.12.1999 19.04.2001 Fontana (Val Pontirone)

0

-50 (mm)

-100

-150 displacement -200 9 LOS 20786 -250

31.01.1993 15.06.1994 28.10.1995 11.03.1997 24.07.1998 06.12.1999 19.04.2001 Fontana (Val Pontirone)

10

-10 (mm)

-30

-50 displacement -70

LOS 1 21856 -90

31.01.1993 15.06.1994 28.10.1995 11.03.1997 24.07.1998 06.12.1999 19.04.2001 Fontana (Val Pontirone) Biasca - Malvaglia Areas prone to deep landslides in Ticino _ Scated + 23º Pontirone from nadir Fontana

Svall Mean displacement Canvasgia rate 1995-2000 ERS SAR data in descending -5 mm/year +1 mode Pontirone

Strozzi, 2004 -5 mm/year +1 _ + 23º from nadir Mean displacement rate 1995-2000 ERS SAR data in descending mode Malvaglia - Scated _ + 23º from nadir

Strozzi, 2004

-5 mm/year +1 Mean displacement rate 1995-2000 ERS SAR data in descending mode Loderio - Semione Areas prone to deep landslides in Ticino

_ + 23º from nadir

Mean displacement rate 1992-2000 ERS SAR data in ascending mode -5 mm/year +1 Loderio _ Strozzi, 2005 + 23º from nadir

Mean displacement rate 1992-2000 ERS SAR data in ascending mode -19 mm/year +1 Loderio _ Strozzi, 2005 + 23º from nadir

Mean displacement rate 1992-2000 ERS SAR data in ascending mode -19 mm/year +1 Areas prone to deep landslides in northern Ticino

Airolo - Val Canaria

Campo Vallemaggia Airolo - Val Canaria JERS 19960620 19960916

_ + 35º from nadir Strozzi, 2005 (+5.75 cm) -! +! (-5.75 cm)

JERS 19960803 1:50’000 19960916 Val Canaria JERS 19960620 19960916

_ + 35º from nadir Strozzi, 2005 -5 cm +2

JERS 19960803 1:50’000 19960916 Campo Vallemaggia

-! _ +! + 35º from nadir -5 cm/88d +2 JERS 19960620 19960916 19960621 19960917 Vertical superficial movements from 04-05.1995 Thüring, 2001 to 06.1996 (from M. Thüring) Campo Vallemaggia Settlements from leveling surveys along the main road between 1992 and 2002

-5 cm/88d +2 20/21.06.96 16/17.09.96 04.06.96 to 24.10.96 scaled to 88 days 2 0 1

) 0 -1 m ) c ( m t -1 c -2 ( n

t e n

m -2 e e -3 m c a e l -3 c p a s l -4 i p d -4 s

i l d a c l -5 i -5 t a r c i e t r V -6 -6 e -7 V -7 -8 0 5 10 15 20 25 30 35 40 45 -8 6 7 8 10 10A 11 13A 15 16 18 19 20A 21 22 23 24 25 26 27 28 Position Benchmark Conclusions ! SAR Interferometric Point Target Analysis of Slope Instabilities in the Community of Biasca, Switzerland, was presented ! Important information are retrieved with IPTA using ERS C-band SAR data over large sparsely vegetated areas with numerous exposed rocks ! The validation of the ITPA results with high quality geodetic data demonstrated a very good accuracy of the satellite SAR-based observations for low displacement rates of 1 to 2 cm/year ! Over forested areas and for moderate to high displacement rates IPTA failed to retrieve displacement information ! The use of L-band SAR data reduces some of the limitations of differential SAR interferometry, in particular signal decorrelation induced by vegetation cover and rapid displacements ! Acknowledgments