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Geology

Unlocking the secrets of the Kameni Islands in Santorini, Greece

P. Nomikou, M.M. Parks, D. Papanikolaou, D.M. Pyle, T.A. Mather, S. Carey, A.B. Watts, M. Paulatto, M.L. Kalnins, I. Livanos, K. Bejelou, E. Simou, I. Perros (2014). The emergence and growth of a submarine volcano: The Kameni islands, Santorini (Greece). GeoResJ, 1–2: 8-18.

In Geology 101, professors aim to teach the overarching concept that the present is the key to the past.  In other words, natural processes that happen in the modern world would have functioned the same way in the distant geologic past. For volcanologists, this means that volcanic events occurring now can help interpret what happened in the past, and vice versa. This applies to the recent work by Nomikou et al. about the emergence and growth of the Kameni Islands in Santorini, Greece (Fig. 1).

Figure 1. Location of Santorini, Greece in the Aegean Sea.

Figure 1. Location of Santorini, Greece in the Aegean Sea.

The analysis of lava flow morphology improves our understanding of historical events by providing insights into the evolution of flow fields, effusion rates and other properties like yield strength, a measure of critical shear stress allowing for viscous lava flow. For instance, morphology of lava flows are closely linked to lava compositions, like silica content implying a particular lobe width. This means that you could estimate lava’s silica content by measuring the width of its dominant lobes – a very valuable tool for primary investigations by remote sensing.

Nomikou et al combine a robust onshore LiDAR dataset with high-resolution swath bathymetry data, to determine for the first time, the morphology of the entire subaerial and submarine volcanic structure of the islands (Fig. 2). The power of this information is that it refines the volume estimates of past eruptions, which may be used to forecast the size of future volcanic events at Santorini.

Figure 2. Combined high-resolution bathymetry and topographic LiDAR dataset.

Figure 2. Combined high-resolution bathymetry and topographic LiDAR dataset.

The resulting digital elevation model is the highest resolution dataset produced of Santorini since Druitt et al. in 1989. It not only shows three distinct basins that form separate depositional environments, but also shows intricate details of the surface morphology of young dacite lava flows, cones and domes, from which important information can be extracted. Examples include:

  • Proof of a previously hypothesized fault/fracture zone that controls all past and present vent locations
  •  A ridge previously thought to be composed of young lava domes may instead be a ridge of older rocks isolated by collapse events
  • New distribution of slope magnitudes indicate the relatively young age of volcanic activity
  • New volumetric estimates for each historic flow
  • Previously unidentified submarine lava flows and cones
  • Pāhoehoe and ‘a’ā flows hit transition from air to water with the former becoming arrested, while the later continues unchanged; meaning, the marine transition had little impact on the reduction of flow length for blocky dacite flows.
  • Flows originally attributed to the 1925-1928 eruption now have an unknown origin… sometime after 1707-1711, but before the originally attributed date.

In addition to the above morphological discoveries, new calculations of yield strength for onshore lava flows are approximately twice as large as the estimates reported in a 2006 study. The increased yield strength may reflect the transition of flows from subaerial to submarine.

Lava flow outlines for historic lava flows in the vicinity of the Kameni islands. The top image shows new onshore/offshore lava flow outlines. The bottom image shows lava flows mapped in older studies (white contours), while the black outline shows the expanded flow extent mapped during this study.

Lava flow outlines for historic lava flows in the vicinity of the Kameni islands. The top image shows new onshore/offshore lava flow outlines. The bottom image shows lava flows mapped in older studies (white contours), while the black outline shows the expanded flow extent mapped during this study.

The analysis of lava flow volumes revealed almost twice the average rate that would be calculated by deriving onshore data alone. An important note made by Nomikou is that the “rest period” (aka pre-eruption rate) between eruptions also determines the volume of lava extruded. This is critical because the current pre-eruption period is ~75yrs to date, meaning they can predict the volume of lava to be next erupted and for how long the eruption can take place, if an eruption occurred in the next few years.

This study does an excellent job of highlighting the benefits of combining high quality LiDAR data with high-resolution bathymetric data for determining the history and rheology of partially submerged volcanic islands. Data sets like this applied elsewhere will unveil the keys to unlock more of Earth’s past, and maybe allude to what lies in the future.

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