lecture1

Physical Volcanology CourseLecture 1Dr. Oleg MelnikInstitute of MechanicsMoscow State University: 

Physical Volcanology Course Lecture 1 Dr. Oleg Melnik Institute of Mechanics Moscow State University

Lecture 1: Introduction: 

Lecture 1: Introduction Volcanic facts. Types of volcanic eruptions and controlling parameters. Structure of the flow in volcanic conduits for explosive and extrusive eruptions. Physical properties of magma and volcanic systems: density, temperature, pressures, water content. Rheology of magma, model for Newtonian liquid and non-Newtonian properties of magma.

Volcano facts: 

Volcano facts How many? 1511 volcanoes in last 10000 years The biggest? > 80,000 km3, Mauna Loa (Hawaii) The highest? 6,887 m, Ojos del Salado (Chile) The biggest eruption? 2,500 km3, Yellowstone, 2.2 Ma (USA) First volcanologist? 79 AD - Pliny the Younger Total deaths? 238,000 (1600-1982)

Deaths by country: 

Deaths by country

Slide5: 

Volcano geography 1. Divergent margins 2. Convergent margins 3. Intraplate 4. Hotspots

Slide7: 

Plate tectonics and magma composition 1. Divergent margins: Plate separation and decompression melting -> low volatile abundance, low SiO2 (~50%), low viscosity basaltic magmas (e.g. Krafla, Iceland) 2. Convergent margins : Mixtures of basalt from the mantle, remelted continental crust and material from the subducted slab. High volatile abundance, intermediate SiO2 (60-70%), high viscosity andesites and dacites (e.g. Montserrat, West Indies) 3. Intraplate `Hot-spot` settings: A. Oceanic: Mantle plumes melt thin oceanic crust producing low viscosity basaltic magmas (e.g. Kilauea, Hawaii) B. Continental: Mantle plumes melt thicker, silicic continental crust producing highly silicic (>70% SiO2) rhyolites (e.g. Yellowstone, USA)

Slide8: 

Types of volcanic eruptions Explosive Gas-particle dispersion flows out of the vent Extrusive Lava flows of domes

Explosive volcanic eruptions: 

Explosive volcanic eruptions

Eruption size distribution: 

Eruption size distribution

The Volcanic Explosivity Index: 

The Volcanic Explosivity Index

VEI damages: 

VEI damages VEI 0: quiet, effusive eruptions of lava; typically a threat to local property only VEI 1-3: progressively more violent explosive eruptions capable of local damage VEI 4-5: moderate explosive eruptions capable of regional damage and disruption VEI 6-7: large to gigantic explosive eruptions capable of global impact through climate modification VEI 8: super-eruptions capable of severe global climate modification

Slide13: 

Several small explosive eruptions every year. Moderate explosive events occur every decade or so and have regional impact Large explosive eruptions have return periods of a century or more ~2 VEI 8 events every 100 millennia

Extrusive eruptions : 

Extrusive eruptions Lava flows Lava domes Photo: Copyright Marco Fulle  -  Stromboli On-Line  -  http://stromboli.net

Structure of the flow during explosive eruption: 

Structure of the flow during explosive eruption

Structure of the flow during extrusive eruption: 

Structure of the flow during extrusive eruption

Physical properties of magma: 

Physical properties of magma Magma: melt + crystals + gas. Melt: Temperature 800-1300 оС, pressure 103 -10-1 MPa, Viscosity 102 -1012 Pa•s. Crystals: size 10-7-10-1 m, number density up to 1017 m-3, fraction up to 95 %. Gas: H2O - 60-95, CO2- 0-35%, mass fraction 0.1-7 %. Ascend velocity: V =10-4- 500 м/c. Special features: high viscosity, strongly dependent on chemical composition and temperature, gas solubility and diffusion, complicated crystal growth kinetics.

Magma rheology: 

Magma rheology m - shear viscosity Viscosity depends on: chemical composition - more SiO2 - more viscous Temperature - higher temperature - less viscous Water content - higher water content - less viscous Crystal content - higher crystal content - more viscous

NonNewtonian rheology: 

NonNewtonian rheology Bingham Power-law fluid Newtonian Shear stress(force) Yield strength Strain rate (velocity)

Conclusions: 

Conclusions Origin of volcanoes Types of volcanic eruptions and controlling parameters What happens in volcanic conduit? Introduction to rheology