# Has the Average Volume of Volcanic Emissions Been Constant Since the Last Major Fluctuation?

Are total volcanic emissions worldwide constant, or do they rise and fall? We know there are large fluctuations on a scale of tens of millions of years, but is the total volume of emissions stable on a scale of tens of thousands, the last ten thousand in particular? The last major increase that I know of was shortly before the extinction of the dinosaurs and according to some geologists was the cause of the extinctions at the end of the Cretaceous, but I suspect there have been further significant episodes of volcanism since then.

• Oct 20 '19 at 20:39

• At ocean ridges, studies show a steady rate of oceanic crust production during the Cenozoic. There have been fluctuations before, maybe due to the breakup of Pangea or other major tectonic events. The present volcanic production rate is ~20 km$$^3$$ per year.
• At volcanic arcs, it is harder to constrain because of the poor preservation of volcanic material. Tephra layers found in deep sea drilling cores show some peaks in explosive activity "in the Quaternary (0-5 Ma), the middle Miocene (c. 13-17 Ma), and potentially the Eocene (c. 37-42 Ma)". This is not well explained. There is also a shorter term variability due to deglaciation episodes: mass unloading depressurize magmatic systems. A conservative estimate of the modern output is 0.5 km$$^3$$ per year.
• Finally, Large Igneous Provinces (LIPs) are very episodic (long-term average of one LIP every 10-20 Ma) but they emit a large volume (generally > 1 million km$$^3$$) in a relatively short period of time (a few million years). LIP emplacement coincide with major mass extinction events.