EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Bridging the gap from caldera unrest to resurgence

Valerio Acocella
Valerio Acocella
  • Università Roma Tre, Dipartimento Scienze, Roma, Italy (

Calderas often inflate up to a few metres for weeks to years, which is evidence of short-term unrest. Some calderas also show larger uplift (up to a thousand metres), achieved over the long-term (hundreds to thousands of years), manifest by a resurgent dome or block. How the short-term inflation relates to long-term resurgence is still poorly understood, even though established views consider the two processes distinct. This study exploits the longer deformation time series now available for several calderas, as well as the better understanding of magmatic processes and their evolution, to try to bridge the gap between these two scales of uplift. Available data challenge established views, suggesting that resurgence, rather than being produced by constant or continuous uplift, is the net cumulated result of tens to thousands distinct episodes of inflation, even interrupted by deflation episodes, as observed on short-term unrest. These inflation episodes are ascribed to distinct pulses of shallow magma emplacement, with most of the magma remaining intruded, especially in felsic calderas. This supports an incremental growth of magmatic systems, consistently with that observed below resurgent calderas and what is inferred for plutons. Comparing the uplift (as expression of the intrusive record) and eruptive histories or resurgent calderas opens new exciting research paths to understand the causal relationships between intruded and erupted magma at a given caldera, thus enhancing its long-term eruptive forecast.

How to cite: Acocella, V.: Bridging the gap from caldera unrest to resurgence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11047,, 2020

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Presentation version 1 – uploaded on 29 Apr 2020
  • CC1: Questions and answers from the live chat during EGU2020, Michael Heap, 11 May 2020

    Q: What is the maximum displacement ever observed during a caldera unrest within months/year?

    A: Metres per year

    Q: Always nice to try to link long term and short term observations! Could you just explain a bit more what you mean by the term « resurgence » for calderas?

    A: Resurgence consists of the uplift of up to ~1 km of the caldera floor over hundreds to thousands of years (Galetto et al., 2017, and references therein). The duration and uplift rate of resurgence are usually poorly constrained, being at best geologically inferred with a total amount of uplift over a given estimated period (often tens of thousands of years), which may be longer than that of effective uplift. In a very few resurgent calderas (Campi Flegrei; Toba, Sumatra; Siwi, Vanuatu; Iwo-Jima, Japan) more detailed information on the evolution of the vertical deformation highlights discontinuous phases of uplift, even alternated with subsidence episodes (Chen et al., 1995; De Silva et al., 2015; Marturano et al., 2018).

    Q: Could you indicate resurgence  in the graph on slide 3?

    A: Resurgence is the WHOLE curve!

    Q: Is there any shorter-term physical evidence against your argument - e.g. that resurgence and unrest are separate processes?

    A: I could say nothing I am aware of, but I may be biased

    Q: Is the formatiuon of post-collapse intrusive complexes ansd thickenimng of the crust a form of resurgence in your view?

    A: Nice question: resurgence as we know it is defined at the surface. If these processes you mention have an evident and long-term surface expression, and occur at the level of the magma chamber or above, they may well be.