Monitoring Volcanoes & Predicting Eruptions. I.G Kenyon

Transcription

1 Monitoring Volcanoes & Predicting Eruptions I.G Kenyon

2 Why Monitor? At least 200,000 people killed by volcanoes over the last 500 years

3 Why Monitor? 500 active volcanoes on land 10% of world population live on their flanks (640 million)

4 Major Eruptions In the last 2000 years 1815, , 1985 Earthquakes kill far more people than volcanoes

5 Monitoring USA - Where? Hawaiian Volcano Observatory (HVO) Cascades Volcano Observatory (CVO) Alaskan Volcano Observatory (AVO)

6 Monitoring Where? Italy Japan New Zealand The Philippines Russia Most active volcanoes are not monitored

7 Monitoring Techniques Volcanocams Seismic studies Gas Analyses Ground Deformation Gravity Surveys Hydrological Surveys Electrical/Magnetic Surveys

8 Monitoring Sakurajima, Japan

9 Monitoring Techniques - Volcanocams On Stromboli in the Aeolian Islands a surveillance camera has been installed on the peak of the volcano The camera transmits real-time images of the volcano s activity 24 hours a day to a monitoring centre in Catania where the pictures are analyzed

10 Volcanic Seismic Activity Seismic Analysis Centre in the Vesuvian observatory in Naples, Italy Transmission stations that collect seismic data have been set up on Vesuvius, Campi Flegrei and the island of Ischia and the collected information is studied here

11 Volcanic Seismicity 3 major types of seismic information Short-period earthquakes are like normal fault related earthquakes. They are caused by magma forcing its way upwards and fracturing brittle rock in the process. Long-period earthquakes indicate increased gas pressure in the volcano s plumbing system. Analagous to the clanging sometimes heard in your home s plumbing system. Harmonic tremor occurs due to sustained movement of magma below the surface often as it is vibrating or pulsating within the feeder pipe or conduit.

12 Volcanic Seismic Activity Prior to eruptions, many earthquakes occur which get progressively shallower Earthquakes are caused by magma forcing its way towards the surface and fracturing the surrounding rock as it migrates upwards Some earthquakes are due to harmonic tremor where the magma is vibrating within the conduit

13 Volcanic Seismic Activity Portable seismometer for registering earth tremors in the field Seismic tomography has been used on Vesuvius for the last decade In addition to monitoring actual seismic activity around volcanoes, artificial events using explosives are employed to build up a 3 dimensional picture of the structure and plumbing of the magmatic system within the volcano

14 Major Gases given off by Volcanoes Over 80% is water vapour Carbon Dioxide, Sulphur Dioxide, Hydrogen, Hydrogen Sulphide and Hydrogen Chloride make up the bulk of the remainder

15 Gas Emissions Fully automatic gas sampling equipment set up in a fumarolic area on the island of Vulcano, Italy Total amount of gas released increases prior to an eruption, the sulphur dioxide proportion increasing most dramatically

16 Gas Emissions in Rambleta crater at the summit of Mount Teide, Tenerife Acicular (needle-like) crystals of yellow sulphur and white alunite are precipitated around the fumaroles Fumaroles belch out a mixture of water vapour, carbon dioxide and sulphur dioxide

17 Instruments used to analyse Gas Emissions COSPEC Correlation spectrometer to measure the amount of sulphur dioxide. These may be mounted on a tripod, on a vehicle or attached to an aeroplane/helicopter FLYSPEC miniature version of COSPEC can be attached to a hard hat or back pack that LI-COR Infra-red analyzer to measure the amount of carbon dioxide in a volcanic plume FTIR Fourier Transform Infrared Spectrometer continuously samples gas in a volcanic plume GASPEC measures carbon dioxide in a volcanic plume

18 Monitoring Gas Emissions COSPEC mounted on a vehicle COSPEC Correlation Spectrometer continuously monitors sulphur dioxide emissions from active volcanoes COSPEC mounted on an aeroplane COSPEC Instrument

19 Monitoring Ground Deformation Traditional Methods surveying by levelling, theodolite surveying EDM - Electronic Distance Measurement using infrared/laser Tiltmeters record changes in angle of slope GPS Global Positioning Systems InSAR Interferometric Synthetic Aperture Radar using satellite measurements

20 Measuring EDM distance to Mount St.Helens Lava Dome A target on the west side of the dome was moving 2cm per day 2 weeks before the May 14 th 1982 eruption; movement increased to about 200cm per day by May 13 th. Such accelerations were frequently used to predict eruptions in 1982

21 Monitoring Equipment Locations around Mount St.Helens

22 Measuring Ground Deformation A B C Typical Hawaiian Pattern A - Volcano begins to inflate B - Inflation reaches its peak C - Eruption followed by deflation

23 Monitoring Mauna Loa and Kilauea, Hawaii Stars show the location of deep boreholes on Mauna Loa where new monitoring equipment has been installed Each borehole contains: An ultra-sensitive strainmeter A three-component broadband seismometer A strong motion sensor Tiltmeters may be added high in each borehole later this year

24 Monitoring Mauna Loa and Kilauea, Hawaii Cross section showing installation of a strainmeter and seismic package on Mauna Loa The strainmeter is encased in expansive grout m below the surface The seismometers are encased in cement 10-20m above the strainmeter The strainmeter is installed below the steel casing as it must be secured to the surrounding rock so that it can sense the pressure being exerted on the rock Strainmeters are also known as dilatometers

25 Monitoring Mauna Loa and Kilauea, Hawaii A strainmeter is a stainless steel pipe 3m long and 10cm in diameter, filled with silicon fluid As moving magma or earthquakes cause the ground to change shape, the dilatometer is squeezed like a balloon The amount of strain is determined by measuring the flow of the silicon fluid into or out of the dilatometer into a secondary reservoir The instruments are very sensitive and can even detect small deformations due to passing weather fronts and the gravitational pull of the sun and the moon, These changes are filtered out by analysis software, and what is left is a measure of the deformation of the ground

26 A three-component broadband seismometer The size and cylindrical shape of the instrument are governed by the shape and diameter of the drill hole Horizontal Sensors Vertical Sensors These are just miniature versions of the seismic sensors placed at the earth s surface

27 Monitoring Mauna Loa and Kilauea, Hawaii The DOSECC drilling rig on the northern flank of Mauna Loa at 3,350m elevation. Mauna Kea rises above the clouds in the background Drillers attach a new length of pipe before coring another section of basalt

28 Monitoring Mauna Loa and Kilauea, Hawaii The cored rocks are examined and logged by scientists from the Hawaiian Volcano Observatory (HVO) and from The Centre for the Study of Active Volcanoes (CSAV) These cores give scientists a record of the eruptive history of Mauna Loa volcano close to its rift zones

29 Monitoring Mauna Loa and Kilauea, Hawaii A solid section of basaltic rock was needed to firmly anchor the strainmeters After a depth of m was drilled the basalt encountered was homogenous and had few fractures Basalt suitable to house the strainmeter

30 Monitoring Mauna Loa and Kilauea, Hawaii An array of surface electronics connect to the instruments in the borehole. The photo below is a completed installation at Hokukano Ranch on the west flank of Mauna Loa Expansive grout being poured into the hole after the strainmeter to anchor it to the surrounding rock

31 Monitoring Changes in Gravity Changes in gravity can be used to estimate subsurface movements of water or magma Below-gravity record from Masaya Volcano Above-Lacoste & Romberg micro-gravity meter. The station consists of a survey pin driven into the bedrock-in this case part of a pahoehoe lava flow

32 Hydrological Monitoring Level and temperature of groundwater in boreholes Monitoring of lake levels Monitoring of stream discharges Coldwater Lake Gauging Station Monitoring of water quality Monitoring of stream sediment loads River channel surveys to measure bank and channel erosion and channel deposition at specific locations

33 Hydrological Monitoring Coldwater Lake Overflow Channel Debris Dam Overflow channels have been built at Castle and Coldwater Lake to stabilise water levels and prevent overtopping of the debris dams

34 Electrical and Magnetic Surveys Deviations in local electrical and magnetic fields are responses to pressure and stresses are caused by the subterranean movement of magma. Mount Etna has 5 automated magnetic monitoring stations and data collected has been used to predict eruptions from 2001 onwards

35 Computer Modelling of Volcanic Hazards 90% 80% 70% Likelihood of roof collapse (%) Satellite image of the area around Vesuvius with superimposed isolines to indicate areas where the accumulated ashfall would be more than enough to cause the collapse of the roofs of homes

36 Mount Rainier, Cascades, USA Hazard Zonation Map Collecting data from previous eruptions allows a detailed picture of potential hazards from future eruptions to be established The map shows areas likely to be at risk from lava flows, pyroclastic flows and lahars Contingency plans are formulated from this data and may involve evacuation and protection measures

37 Mount Pinatubo Map to show volcanic hazards associated with the 1992 eruption Depth and distribution of ashfall, deposits from pyroclastic flows and volcanic mudflows (lahars) Building in the lower pats of the valleys affected by lahars is now to be restricted

38 Predicting Eruptions Building up a detailed knowledge of past eruptions allows patterns or cycles of activity to be identified. From this predictions of future eruptions may be made

39 The End