A 1600 year-long sedimentary record of tsunamis and hurricanes in the Lesser Antilles (Scrub Island, Anguilla)

Abstract

The Lesser Antilles are a densely populated and a very touristic region exposed to many short-term hazards such as hurricanes and tsunamis. However, the historical catalog of these events is too short to allow risk assessment and return period estimations, and it needs to be completed with long-term geological records. Two sediment cores were sampled in March 2018 in a small coastal lagoon on Scrub Island (north eastern Caribbean). Here, we present sedimentological, geochemical, microfaunal and chronological analyses that enabled us to identify 25 sandy layers resulting from high energy marine floods. Two of these layers were interpreted as tsunami deposits based on sedimentological and geochemical evidence. The most recent deposit is associated with the transatlantic tsunami triggered by the 1755 AD Lisbon earthquake. The older is the thickest sandy layer recorded in the lagoon and is dated at 1415 cal. AD (1364-1469 cal. AD). This event was recorded in both the northern and the southern part of the Caribbean, with its large extent supporting a tsunamigenic origin. The 23 remaining sandy This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology 2 layers were interpreted as resulting from hurricanes, with the three most recent layers being associated with historical hurricanes. This new 1600 year-long reconstructed chronicle, has been compared to other published hurricane chronicles from the region. Scrub chronicle is the most eastern site and displays similarities with that of the Bahamas, while it is in antiphase with that of the north eastern US coast. This regional comparison may provide evidence of a latitudinal forcing for the hurricane tracks through time in relation to climate fluctuations.

A Review of Event Deposits in Lake Sediments

“…It is not surprising that the vast majority of coastal lake paleotsunami studies are along subduction zones, which are infamous for triggering the most destructive and widespread tsunamis during megathrust earthquakes. The first studies appeared in the nineties from Japan [121] and Vancouver Island [122], and more recent examples include coastal lakes along the Japan-Nankai [123], Japan-Honshu [116], Cascadia [124], Chile [125], Lesser Antilles [16,126] and eastern Mediterranean [127,128] subduction zones, and in Sri Lanka from Indian Ocean tsunamis [129]. Apart from such subduction zone tsunamis, the Storegga Slide tsunami has also been recorded in Norwegian coastal lakes [130,131].…”

“…However, it also depends on the available material in the barrier. The spatial distribution of these deposits typically shows a strong gradient, with high-energy facies concentrated near the inflow of the tsunami and finer-grained basal facies away from the inflow [16,124,125,129]. The deposits regularly contain large organic remains; shell debris, e.g., [128,129,134]; and marine diatoms or foraminifera [16,121,124,134], the latter two of which are clear indicators of marine origin.…”

“…The spatial distribution of these deposits typically shows a strong gradient, with high-energy facies concentrated near the inflow of the tsunami and finer-grained basal facies away from the inflow [16,124,125,129]. The deposits regularly contain large organic remains; shell debris, e.g., [128,129,134]; and marine diatoms or foraminifera [16,121,124,134], the latter two of which are clear indicators of marine origin. In contrast, in a coastal lagoon, which is already brackish, the terrestrial (barrier) origin of the deposits may be the main indicator for a tsunami deposit [127].…”

“…In contrast, in a coastal lagoon, which is already brackish, the terrestrial (barrier) origin of the deposits may be the main indicator for a tsunami deposit [127]. The presence or absence of salt coating on sand grains, respectively indicating a barrier or lower-shoreface origin for sand grains, could also be used as a criterion to identify tsunami (reworking both barrier and shoreface sediments) from hurricane (mostly reworking barrier sediments) deposits [16]. Finally, different pulses of coarser-grained material within the general fining trend (e.g., layers with mud clasts or a sharp increase in grain size) have been attributed to separate uprush events and thus tsunami waves in several studies [125,130,131].…”

“…The first step in reconstructing event deposit chronicles from lake sediments is to identify and characterize event deposits, followed by the attribution of a sedimentary facies and/or deposit geometry to a triggering mechanism. Indeed, a given lake sediment sequence often records a combination of natural hazards (Figure 1), such as floods and earthquakes, e.g., [16][17][18][19][20], floods and avalanches [12], floods and GLOFs [21], floods and tsunamis [22], hurricanes and tsunamis [16], earthquakes, volcanic eruptions, and floods [23], etc. These event deposits are generally recorded as turbidites, debrites, homogenites, slumps, and mass-transport deposits, which each have their own sedimentological signature.…”