by “Hearts on deck!”
For two months, whenever I heard that cry, I would run up to the deck of the Secret JOIDES to watch the crew pull up a 30-foot (10-meter) cylindrical tube filled with layered, colorful rock and sediment drilled from the bottom of the sea. under our ship.
In the winter of 2022, I spent two months cruising the southern Aegean aboard the International Ocean Discovery Program’s Secret JOIDES as part of IODP Expedition 398. My geologist colleagues and I used the former oil exploration ship this to drill deep into the bottom of the sea and reveal. the volcanic history of the area off the coast of Santorini, Greece.
As a scientist who studies the chemistry of volcanic rocks, I use my expertise to correlate volcanic sediments with the eruption that caused them and to understand the conditions of magma at depth beneath a volcano and during an eruption.
Our expedition’s drilling of the seabed revealed a massive, but previously unknown, volcanic eruption that occurred over 500,000 years ago. This discovery increases our understanding of volcanic activity in the chain of volcanoes that comprise the South Aegean Volcanic Arc, which will allow a more accurate analysis of hazards in this region.
Building a fuller volcanic history
Archaeologists have long been fascinated by the eruption of Santorini since the Late Bronze Age around 1600 BCE. This eruption is related to the decline of the Minoan civilization on the nearby island of Crete. Geologists are also of considerable interest in the region, due to the fluctuating volcanic and seismic activity in this area which has around 15,000 residents and attracts around 2 million tourists per year.
Although there is considerable documentation on the ground regarding the Santorini volcano, scientists know that this record is incomplete. On land, erosion, vegetation and further eruptive events often cover or seal the older volcanic deposits, which have a fractured history. The deep-sea drilling enabled by the IODP’s JOIDES Resolution gives researchers access to a geological record rarely preserved on land.
After a volcanic eruption, pyroclastic materials – pieces of rock and ash formed during the eruption – settle through the water column to collect on the sea floor. Clays and biological material, such as the shells of tiny marine organisms, are continuously raining down, limiting the volcanic rock deposits. This process preserves a record of individual eruptions as a single series. Layers build over time, and each successive volcanic event creates an almost continuous chronological record of the region’s volcanic history.
Expedition 398’s mission was to access this deep-sea record to document the extensive history of eruptions in all areas of concentrated volcanic activity.
IODP 398 Trips
IODP Expedition 398 collected drill cores to better understand the volcanic history and recurrence interval of the Santorini, Christiana and Kolumbo volcanoes in this region. The JOIDES Resolution crew drilled 12 locations to a maximum depth of 2,950 feet (900 meters) below the seabed. We recovered more than 11,000 feet (3,356 meters) of total core over 780 cores.
As technicians cut the core into 4½-foot (1½-meter) sections, scientists gathered to see what material had been found. After bringing the cores to surface pressure, the team would split them lengthwise, photograph them, analyze them for physical properties such as magnetic susceptibility, and describe the material. Core loggers measure and record the geological composition of each rock unit within.
While in charge of the geochemical laboratory, I took small samples of multiple layers of volcanic rock and ash to dissolve and analyze their trace element composition. During an eruption, magma crystallizes and mixes with elements in the water and rock it comes into contact with. The resulting chemical changes in the magma are unique to the conditions of that particular eruption. So, once I do the chemical composition of the deposit samples, I can fingerprint their volcanic origin.
Our discovery: The Archaeos Tuff
During the trip, our group of researchers found a thick, white layer of pumice at multiple sites, in different basins. Ship biostratigraphy dated all occurrences of the layer to the same age: between 510,000 and 530,000 years ago. Geochemical correlations suggested that the composition was the same throughout the drill holes as well.
By finding the same layer across these basins, our research team can model the size of the eruption that caused it. We used seismic data collected during the trip to determine that the bulk of the volcanic sediment was about 21 cubic miles (90 cubic kilometers), with a thickness of up to 490 feet (150 meters) in some places. Furthermore, we determined that this layer of volcanic rock was spread over 1,100 square miles (3,000 square kilometers) of this region in the southern Aegean Sea.
Our team named this deposit the Archeos Tuff, from the Greek word archaea for ancient. The name reflects the Greek origin of the rock, as well as the fact that it was much older than much of the volcanic activity we know of on earth.
Based on the characteristics of the Archeos Tuff, we can understand the nature of the volcanic eruption that created it. Its thickness and distribution over a wide area suggest that the Archeos Tuff is the result of a single, high-intensity eruption. The numerous vesicles, or small holes, in the rock indicate that a large amount of gas was released at the same time as the liquid magma. These small bubbles of gas paint a picture of a powerful eruption in which a lot of volatile gas was released very quickly.
But despite its size and obvious equipment, this eruption did not involve any deposits on the ground or large eruptions that were known before. The relative lack of material on land suggests that the eruption is mostly submarine. Once we knew what we were looking for, our team was able to match our newly discovered deep-sea layer of volcanic sediment with several previously unrelated small deposits on land on the islands of Santorini, Christiana and Anafi. The presence of these deposits indicates some breach of the sea surface during the eruption, which again fits our picture of an energetic eruption.
Further study of the composition and age of the Archeos Tuff confirmed the unique nature of the rock deposits left by this eruption. Based on the data we have collected, our team believes that the Archeos Tuff is the result of an eruption six times larger than the Minor Bronze Age eruption, leaving behind rock deposits 30 times thicker. The presence of such a volcanic deposit tells us that the South Aegean Volcanic Arc is more capable of producing large submarine volcanic eruptions than scientists previously recognized.
By identifying the Archaeos Tuff increases what we know about volcanic processes in the southern Aegean Sea. It suggests that there is a greater propensity for hazardous submarine volcanism than previously realized – and that officials need to reassess volcanic hazards to the surrounding population.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by Molly Colleen McCanta University of Tennessee
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Molly Colleen McCanta receives funding from the IODP.
