Volcanoes
Italian Volcanoes
- Etna
- Location: Sicily
- Diameter: 35 km; Elevation: 3,295 m
- Eruptive style: primarily Strombolian
- Active today; continuously since classical times
- Catania almost destroyed in 1669
- Deposits
- Trachybasalt (high alkali basalts)
- Trachyandesite
- Stromboli
- Location: Aeolian Islands north of Sicily
- Diameter: 3.5 km; Elevation: ~ 1,000 m
- Eruptive style: Strombolian
- Active today; continuously since classical times
- Started 200,000 years ago
- “Lighthouse of the Mediterranean”
- Deposits
- K-rich basalts
- Basaltic andesite
- Vesuvius
- Location: ~ 9 km east of Naples
- Diameter: 6 m; Elevation: 1,281 m
- Stratovolcano in Campanian volcanic arc
- Eruptive style: Plinean (explosive!) and Strombolian
- Deposits: lava pyroclastic flows, ash, pumice
- Notable eruption in 79 AD destroyed Pompei and Herculaneum
- Last major eruption: 1944, eruptive more than 50 times
- Phlegraean Fields
- Location: West of Naples
- Diameter: 15 km; Elevation: 458 m (maximum)
- Large caldera with smaller calderas and small volcanoes
- Eruptive style: varied in its history
- Originally Plinean (explosive): Capannina Ignimbrite
- 1538 Mt Nuova (“New Mountain”): cinder cone
- Deposits: ash-flows, tuffs, pyroclastic deposits, K-basalt, alkali-trachyte, phonolite
- “Brayseism”: vertical ground motions
- Documented since classical times
- Still going on today
Auvergne and related issues
- Various features
- North-south line of “puys” volcanic cones
- Flows into adjacent valleys (lying to east or west)
- Stratovolcanoes to south
- Three interpretive questions for geognosts
- Origin of Magmas
- Observe: volcanic cone sitting atop granite plateau
- No coal available, so infer magma underlying granite
- Implies heat at depth
- Origin of Basalts
- Field relations allow (relatively recent) basalt beds to be traced to volcanic cones
- Basalts underlain by “baked” soils
- Infer origin as lava flows
- Erosion and Modification of deposits
- Cones show a sequence of morphologies
- Largely intact cinder cones
- Eroded, breached cones with loose scoria removed
- Remnant bases; craters largely eroded
- Flows also change
- Well-preserved flow with little erosion; traceable to intact cones
- Flows not connected to cones; upper surfaces eroded
- Remnants form flat, isolated plateaus
- Cones show a sequence of morphologies
- Origin of Magmas
- Two major insights
- If Auvergne basalt are igneous, traditional geognost interpretation of volcanics (due to burning coal) not correct.
- Modification of interpretive model
- Erosion of cones and flows suggest long history that can be subdivided using the field relations and relative implied timing
- Insight into subdividing “recent” earth history in detail
- If Auvergne basalt are igneous, traditional geognost interpretation of volcanics (due to burning coal) not correct.