Understanding and forecasting phreatic eruptions driven by magmatic degassing.

Area of Science:

• Volcanology
• Geochemistry
• Geophysics

Background:

• Phreatic eruptions are hazardous volcanic events driven by magmatic and hydrothermal processes.
• Understanding eruption mechanisms is crucial for hazard assessment and mitigation.
• Active phreatic systems in Costa Rica (Turrialba, Poás) provide valuable case studies.

Purpose of the Study:

• To define and differentiate two endmember types of phreatic eruptions based on magmatic gas input and hydrothermal system interaction.
• To investigate precursory signals for improved forecasting of phreatic eruptions.
• To synthesize data from significant phreatic systems for a comprehensive analysis.

Main Methods:

• Classification of phreatic eruptions into two types: phreato-vulcanian (type 1) and phreato-surtseyan (type 2).
• Analysis of data from active phreatic systems, including those in Costa Rica.
• Examination of precursory signals such as very long period events, banded tremor, and gas ratios (H₂S/SO₂, CO₂/SO₂).

Main Results:

• Type 1 (phreato-vulcanian) eruptions originate from deeper, sealed hydrothermal systems and are generally more energetic.
• Type 2 (phreato-surtseyan) eruptions result from open-vent degassing to shallow hydrothermal systems, characterized by surficial sources.
• Some volcanic systems can exhibit both eruption types, and sealing dynamics influence eruption style.
• Specific precursory signals, including seismic events and gas ratios, were identified as important indicators.

Conclusions:

• Phreatic eruptions can be categorized into two distinct endmember types with differing mechanisms and energy potentials.
• Integrated monitoring of seismic and gas data offers a pathway to accurately forecast phreatic eruptions.
• Understanding the interplay between magmatic gas input and hydrothermal systems is key to predicting volcanic hazards.