1. September 20101Master of Science in Geological & Mining & Sciences Michigan Technological University – College of Engineering Historic Activity Records of Galeras Volcano, Nariño, Colombia A time series analysis example Federica Lanza

2. September 2010Master of Science in Geological & Mining & Sciences2 Volcano Galeras, southwestern Colombia  Most active volcano in Colombia, near the city of Pasto  Stratovolcano (complex volcano)  Andesitic in composition  Long-term extensive hydrothermal alteration  Two major sector collapses (late Pleistocene)  Strike-slip context (Romeral-Buesaco fault system) What kind of Volcano?

3. September 2010Master of Science in Geological & Mining & Sciences3 Main features of eruptions  Main central crater and smaller craters (i.e El Pinta Vent, El Viejo, Baston etc.)  Eruptions (mostly vulcanian type) consist of: - central vent eruptions - explosive eruptions (VEI 2 – 3) - phreatic explosions - lava dome extrusions - radial fissure eruption (1993) Pyroclastic flows Widespread tephra deposits Lava flows (rare) Lahars From Smithsonian – GVN web source From Google Images

4. September 2010Master of Science in Geological & Mining & Sciences4 Eruptive History Spreadsheet: database Data sources: Smithsonian Institution - GVN  34 data points (eruptive events)  Long span of time investigated: from 7050 BC till now (2010)  High dispersion around the mean value  Great uncertainty

5. September 2010Master of Science in Geological & Mining & Sciences5 Assumptions  start date when neither the day nor the month is reported: 15th June or approximately in the middle of the year  stop date when it is unknown: year, month and day have been inferred from dataset  start date and/or stop date when no day (or month) is reported: 1 st of the month in which the eruption has occurred or according to data trend Dataset criteria

6. September 2010Master of Science in Geological & Mining & Sciences6 Time series analysis (I) - Size  Frequency of size or “magnitude” of each eruption  Volcanic Explosivity Index (VEI)  Moderate to moderate-large eruptions Ordered dates

7. September 2010Master of Science in Geological & Mining & Sciences7 Time series analysis (II) – Duration of eruptions  Short duration eruptions  Consistency of data except for one event (1670 peak)

8. September 2010Master of Science in Geological & Mining & Sciences8 Time series analysis (III) – Repose time  BC events included/not included  Decreasing pattern of repose time with time, why? Sampling resolution?

9. September 2010Master of Science in Geological & Mining & Sciences9  Linear relationship between years and interval time between periods of eruption (BC data are not considered)  Changes in the volcano behavior?  Wide range of values  Reliability? Time series analysis (IV) – Repose time

10. September 2010Master of Science in Geological & Mining & Sciences10 Time series analysis (V) – Volume of material emitted  Linear relationship between the volume of material and the duration of activity - short and weak eruptions - short but strong eruptions - very long and vigorous eruptions

11. September 2010Master of Science in Geological & Mining & Sciences11 Problems regarding the data criteria of eruptions  What do we mean by “eruption”  Dating methods  Stochastic process (randomness)  Assumptions  Uncertainty: caution and evaluation of representativeness Photo courtesy of Marta Calvache, August 27,1936 (INGEOMINAS-Observatorio Vulcanológico del Sur).

12. September 2010Master of Science in Geological & Mining & Sciences12 Forecasting based on historical and prehistoric activity Caveats for long-term hazards assessment  Obliteration by subsequent events of older records  Unreliable average repose interval due to the wide range of time intervals between eruptions  Changes in eruption habits  Unprecedented events  Change of hazardous area locations due to changes in the size and shape of volcanoes with time Conclusions

13. September 2010Master of Science in Geological & Mining & Sciences13 Can the Galeras dataset be used for forecasting purposes?  Random pattern in the timing of historical eruptions  No evidence of cyclical behavior  Wide variation in the repose times between eruptions Combine different tools to reduce uncertainty: Monitoring approach & Basic Research Thermal radiation Seismicity Electromagnetic, magnetic data From Seidl (2003)