**4. Discussion**

Normalization of data against Al in the Samoan cores reveals similar characteristic profile trends analogous to the findings in the Little Pigeon Bay study. This includes the identification of a distinct elemental signal of the 2009 tsunami event at Manono and Ma'asina. While data gaps associated with detection limits and low Al count rates are present in each of the profiles, the interpolated plots provide an adequate means to identify distinct elemental signals that are indicative of sudden and/or distinct influences in the coastal landscape.

The 2009 tsunami benchmark signals identified at Manono-uta and Ma'asina are unique in that they were not clearly detected during initial analysis of these cores in [19]. The characteristic signals deeper in the core at Ma'asina probably represent historical tsunamis that are known to, or may have, inundated this site. Potential candidates include the far-field 1960 Valdivia Tsunami, 1957 Aleutian Tsunami, and possibly the local 1917 Samoa-Tonga and far-field 1868 Arica Tsunamis [19] (**Figure 3**).

The lack of benchmark elemental signatures for storm surges in these Islands makes it difficult to associate any of the signals detected in this study with tropical cyclones. Furthermore, the distance of each core site from the shore makes it more likely that the signals detected deeper in the cores are representing older and/or

**33**

**Figure 3.**

*geochronological time markers.*

*Tsunami Elemental Signatures in the Samoan Islands: A Case Study*

unknown tsunami events. However, it is possible that smaller signals than the 2009

*Interpreted tsunami associated strata in the Samoan cores based on elemental signatures and available* 

At Manono-uta, tsunamis to severely inundate this site and leave a signature in the landscape are more likely to be associated with events approaching from southerly directions. It is therefore probable that the characteristic, though weaker, signal observed at 0.45 m depth is representing the local 1917 event, which may have had similar impacts to the 2009 event [21]. However, a definitive correlation is difficult

The relative depth of the AD 1185–1280 (or younger) potential event, denoted by the strong signal at 1.4 m depth in the Lano core, compared with characteristic signals at 1.9 m in the Manono-uta profiles, suggests a possible event association. The depth which these signals occur implies that they are older than the deepest signal exhibited at Ma'asina. However, despite the short core length obtained from Ma'asina, extrapolating the range of available 210Pb time-markers for this site in [19] suggests that the deepest signal could represent an inundation event up to several centuries ago. Furthermore, the signals detected at Ma'asina likely corroborate this embayment providing favorable conditions for preserving evidence of both local

While potentially major regionally and far-field sourced transpacific paleotsunamis have been suggested in the literature [22, 23], a distinct association between such events with the signals detected in the Samoan cores is ambiguous given the limited time markers available. Nevertheless, it is probable that if a major transpacific tsunami sourced at the Tonga-Kermadec zone had impacted the Samoan Islands, it would have left a distinct elemental signal in the landscape similar to, or stronger than, the 2009 signature. The occurrence of strong elemental signals at depth in Manono-uta and Lano suggest that these sites experienced a significant inundation event at some point in the past. Whether these are representing the

benchmark could be representing storm surge inundation.

without chronological time-markers at this site.

and far-field tsunamis to impact this region.

*DOI: http://dx.doi.org/10.5772/intechopen.85639*

*Tsunami Elemental Signatures in the Samoan Islands: A Case Study DOI: http://dx.doi.org/10.5772/intechopen.85639*

**Figure 3.**

*Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques…*

tic signals observed deeper in the cores [8].

and 63% for the Lano and Manono-uta cores, respectively.

associated with the 2016 event directly overlies the pre-inundated sediment surface. This provided a benchmark tsunami signature at this site, with similar characteris-

However, significant data gaps are observed in the Samoan profiles, especially the Lano and Manono-uta cores. These gaps are associated with the Al counts approaching detection limit and/or non-detection. In contrast, the non-detection of Al in the Ma'asina core accounted for only 7% of the total dataset compared with 61

At Manono-uta, distinct elevated signals are observed at ~0.06 m depth for most of the detected elements except Si. The Si trend exhibits a relatively low and stable background elemental signal with no discernable changes in the profile, indicating that offshore and terrestrial sources for Si are not abundant at this site. Manono-uta was inundated by the 2009 tsunami with flow depths up to 2 m in some areas, including the core site in this study, with the elevated signals at the core surface likely representing the elemental signature of this event. Characteristic signals deeper in the profile which appear lower in magnitude than the 2009 signature are likely representing: (1) smaller events; (2) other types of coastal processes (e.g., storm surge or rainfall-related

flooding); and/or (3) artifacts associated with interpolation and matrix effects. Comparable trends are observed at Ma'asina where a distinct elevated signal occurs at ~0.05 m. This site was also inundated during the 2009 tsunami which suggests that the elevated signal is representing this event. 210Pb ages available for this core in [19] suggests that similar signals observed at depth could be representing historical tsunamis such as the 1960 Valdivia tsunami, or storm surges which are

known to have impacts this area (such as the 1991 Tropical Cyclone Val).

At Lano, elevated elemental signals are not apparent at the surface of the core. Compared with the sites at Manono-uta and Ma'asina, this site was not inundated during the 2009 tsunami [15], thus a signal for this event would not be expected. Interestingly, a strongly elevated signal is observed at 1.4 m which is consistent with a distinct calcareous sand unit described in [19]. An available calibrated 14C age of AD 1185–1280 at 1.39 m obtained from plant fragments within this unit [19], indicates that a potentially significant inundation event might have occurred during, or

Normalization of data against Al in the Samoan cores reveals similar characteristic profile trends analogous to the findings in the Little Pigeon Bay study. This includes the identification of a distinct elemental signal of the 2009 tsunami event at Manono and Ma'asina. While data gaps associated with detection limits and low Al count rates are present in each of the profiles, the interpolated plots provide an adequate means to identify distinct elemental signals that are indicative of sudden

The 2009 tsunami benchmark signals identified at Manono-uta and Ma'asina are unique in that they were not clearly detected during initial analysis of these cores in [19]. The characteristic signals deeper in the core at Ma'asina probably represent historical tsunamis that are known to, or may have, inundated this site. Potential candidates include the far-field 1960 Valdivia Tsunami, 1957 Aleutian Tsunami, and possibly

The lack of benchmark elemental signatures for storm surges in these Islands makes it difficult to associate any of the signals detected in this study with tropical cyclones. Furthermore, the distance of each core site from the shore makes it more likely that the signals detected deeper in the cores are representing older and/or

the local 1917 Samoa-Tonga and far-field 1868 Arica Tsunamis [19] (**Figure 3**).

and/or distinct influences in the coastal landscape.

**32**

after, this period.

**4. Discussion**

*Interpreted tsunami associated strata in the Samoan cores based on elemental signatures and available geochronological time markers.*

unknown tsunami events. However, it is possible that smaller signals than the 2009 benchmark could be representing storm surge inundation.

At Manono-uta, tsunamis to severely inundate this site and leave a signature in the landscape are more likely to be associated with events approaching from southerly directions. It is therefore probable that the characteristic, though weaker, signal observed at 0.45 m depth is representing the local 1917 event, which may have had similar impacts to the 2009 event [21]. However, a definitive correlation is difficult without chronological time-markers at this site.

The relative depth of the AD 1185–1280 (or younger) potential event, denoted by the strong signal at 1.4 m depth in the Lano core, compared with characteristic signals at 1.9 m in the Manono-uta profiles, suggests a possible event association. The depth which these signals occur implies that they are older than the deepest signal exhibited at Ma'asina. However, despite the short core length obtained from Ma'asina, extrapolating the range of available 210Pb time-markers for this site in [19] suggests that the deepest signal could represent an inundation event up to several centuries ago. Furthermore, the signals detected at Ma'asina likely corroborate this embayment providing favorable conditions for preserving evidence of both local and far-field tsunamis to impact this region.

While potentially major regionally and far-field sourced transpacific paleotsunamis have been suggested in the literature [22, 23], a distinct association between such events with the signals detected in the Samoan cores is ambiguous given the limited time markers available. Nevertheless, it is probable that if a major transpacific tsunami sourced at the Tonga-Kermadec zone had impacted the Samoan Islands, it would have left a distinct elemental signal in the landscape similar to, or stronger than, the 2009 signature. The occurrence of strong elemental signals at depth in Manono-uta and Lano suggest that these sites experienced a significant inundation event at some point in the past. Whether these are representing the

same event and whether they signify the extent of a major transpacific or a more localized event similar to the 2009 and 1917 tsunamis, is unclear and requires more detailed investigation.

Importantly, due to non-detection of Al and subsequent data gaps, the Lano and Manono-uta sites are only providing true representations of 39 and 37% of their total analyzed profiles, respectively, compared with 93% for the Ma'asina site. While interpolation enables more meaningful elemental profiles to be produced, it is likely that fine-scale signals at Lano and Manono-uta are diluted and not adequately represented. Consequently, the interpretations presented for these sites should be used with care.
