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Case study: volcanic hazards

Case study: volcanic hazards. Introduction to case study: Measuring erosion and sedimentation from multi-temporal DTM’s: Pinatubo volcano.

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Case study: volcanic hazards

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  1. Case study: volcanic hazards Introduction to case study:Measuring erosion and sedimentation from multi-temporal DTM’s: Pinatubo volcano. • Elaboration of geomorphologic maps for the pre- and post-eruption situations, up till 1993. This was done in order to evaluate the changes in the catchment areas and their significance in producing lahars. • Creation of digital terrain models for each year, from which the thickness of pyroclastic flows, and the yearly eroded volume can be calculated. ISL 2004

  2. Study area: Pinatubo ISL 2004

  3. Pyroclastic flow deposits Pyroclastic flow deposits Severe erosion Lahars Lahars ISL 2004

  4. Modelling erosion at Mt Pinatubo ISL 2004

  5. Pre eruption DTM Post eruption DTM Post lahar 1993 DTM Post lahar 1992 DTM Post lahar 1991 DTM ISL 2004

  6. Digital Elevation Models • DTMpre This is a DEM before 1991 • DTMerp This is a DEM showing the situation shortly after the eruption • DTM91 This is a DEM after the first rainy season • DTM92 After the second rainy season • DTM93 After the third rainy season • Plus catchment maps and drainage maps ISL 2004

  7. Flowchart volume calculation ISL 2004

  8. Modelling erosion at Mt Pinatubo ISL 2004

  9. Cross sections ISL 2004

  10. After eruption Thickness:= DTMERP-DTMPRE • positive values: pyroclastic flow deposits • negative values: crater Volume per pixel: Volume=Thickness*Pixelsize Total Volume in map: Aggregate volumes per pixel ISL 2004

  11. ISL 2004

  12. Catchment change after eruption • Total size smaller ?! • Large change from Sacobia to Abacan ISL 2004

  13. Volume calculations • Volume calculations per catchment based on pre- and post eruption catchment boundaries. ISL 2004

  14. After first rainy season • Total erosion Ero91:=if(dtm91<dtmerp,dtmerp-dtm91,0) • Erosion in PF deposits: Eropf91:=if((ero91>0)and(dtm91>dtmpre),dtmerp-dtm91,0) • Erosion in other deposits: Eroot91:=if((ero91>0)and(dtm91<dtmpre),dtmpre-dtm91,0) ISL 2004

  15. After first rainy season • Sedimentation in 1991: Sed91:=if((dtm91>dtmerp,dtm91-dtmerp,0) • Remaining PF material in 1991: Rem91:=if(dtm91>dtmerp,dtmerp-dtmpre,if(dtm91<dtmpre,0,dtm91-dtmpre) or Rem91:=(dtm91-dtmpre)-sed91 and use only the positive values ISL 2004

  16. Resulting maps ISL 2004

  17. ISL 2004

  18. Catchment change after first rainy season • Abacan back to Sacobia : stream piracy ISL 2004

  19. Volume calculations ISL 2004

  20. After second rainy season • Total erosion Ero92:=if(dtm92<dtm91,dtm91-dtm92,0) ISL 2004

  21. After second rainy season • Erosion in PF deposits: Eropf92:=if((ero92>0)and(dtm92>dtmpre)and(dtm92<dtmerp),dm91-dtm92,0) • Erosion in other deposits: Eroot92:=if((ero91>0)and((dtm92<dtmpre)or(dtm92>dtmerp),dtm91-dtm92,0) ISL 2004

  22. After second rainy season • Sedimentation in 1992: Sed92:=if((dtm92>dtm91,dtm92-dtm91,0) • Remaining PF material in 1991: Rem92:=if(dtm92>dtmerp,dtmerp- dtmpre, if(dtm92<dtmpre ,0,if(dtm92> dtmp91, dtm91 -dtmpre,dtm92-dtmpre)) or Rem92:=(dtm92-dtmpre)-sed92 and use only the positive values ISL 2004

  23. ISL 2004

  24. Catchment change after second rainy season • Minor changes ISL 2004

  25. Volume calculations ISL 2004

  26. After third rainy season • Total erosion Ero93:=if(dtm93<dtm92,dtm92-dtm93,0) ISL 2004

  27. After third rainy season • Erosion in PF deposits: Eropf93:=if((ero93>0)and(dtm93>dtmpre)and(dtm93<dtmerp),dm92-dtm93,0) • Erosion in other deposits: Eroot93:=if((ero93>0)and((dtm93<dtmpre)or(dtm93>dtmerp),dtm92-dtm93,0) ISL 2004

  28. After third rainy season • Sedimentation in 1993: Sed93:=if((dtm93>dtm92,dtm93-dtm92,0) • Remaining PF material in 1993: Rem93:=if(dtm93>dtmerp,dtmerp-dtpre ,if(dtm93<dtmpre ,0,if(dtm93>dtmp92 ,dtm92-dtmpre,dtm93-dtmpre)) ISL 2004

  29. ISL 2004

  30. Catchment change after third rainy season • More change Abacan - Sacobia • Large change Sacobia - Pasig due to secondary explosion & stream piracy ISL 2004

  31. Volume calculations ISL 2004

  32. ISL 2004

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