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Somma Volcanoes | Dr John Seach
Somma Volcanoes
A somma volcano is a caldera partially filled by a new central cone, named for Mt. Somma in Italy.
Somma volcanoes (also called somma-stratovolcanoes) represent a composite structure where a collapse caldera is partially filled by renewed central cone growth. The older caldera rim (somma) surrounds a younger stratovolcano.
This page provides an expanded overview of somma volcano formation, characteristics, famous examples, and hazards, compiled by volcanologist Dr John Seach.
A somma volcano is a caldera partially filled by a new central cone, named for Mt. Somma in Italy.
Somma volcanoes (also called somma-stratovolcanoes) represent a composite structure where a collapse caldera is partially filled by renewed central cone growth. The older caldera rim (somma) surrounds a younger stratovolcano.
This page provides an expanded overview of somma volcano formation, characteristics, famous examples, and hazards, compiled by volcanologist Dr John Seach.
Formation and Characteristics
Somma volcanoes form in two main stages:
- Caldera Formation: Large explosive eruption empties magma chamber, causing roof collapse.
- Renewed Activity: Magma rises again, building a new cone inside the caldera.
Key characteristics:
- Structure: Older caldera rim (somma) encircling younger central cone.
- Composition: Typically andesitic to dacitic; explosive history.
- Shape: Horseshoe or circular caldera with steep inner cone.
- Size: Caldera 2–15 km diameter; cone up to several km high.
- Activity: Often highly explosive; flank eruptions common.
Famous Somma Volcano Examples
- Vesuvius (Italy): Classic example; Monte Somma rim surrounds Vesuvius cone; destroyed Pompeii in 79 AD.
- Medvezhia (Kurile Islands, Russia): Well-preserved somma with central cone.
- Kolokol Group (Kurile Islands, Russia): Somma structure with active domes.
- Ebeko (Kurile Islands, Russia): Active somma volcano.
- Urataman (Kurile Islands, Russia): Distinct somma rim.
- Crater Lake (USA): Mount Mazama caldera with Wizard Island cone.
- Santorini (Greece): Caldera with Nea Kameni central islands.
- Toba (Indonesia): Massive caldera with Samosir resurgent dome (similar structure).
Hazards
Somma volcanoes pose severe hazards due to their explosive history:
- Plinian eruptions capable of caldera collapse.
- Pyroclastic flows from central cone or flank vents.
- Ashfall over wide areas.
- Flank eruptions threatening populated slopes.
- Sector collapse and debris avalanches.
Historical events like Vesuvius 79 AD demonstrate catastrophic potential for nearby populations.