166
land sediment, and forams are marine organisms), or they contained forams that
indicated brackish, intertidal environments. The tsunami sediments contained
forams from near-shore and deeper offshore marine environments. They provided
evidence of varying depths of excavation by tsunami waves offshore but also evidence of backwash tsunami flow – mangrove swamp forams that were deposited
seaward during the backwash. What was evident was that, by only using sediment
characteristics or only foraminiferal assemblages, we would not have gotten the full
picture. Both kinds of data together provide the best way to characterize tsunami
deposits, which you can see from my description here can be quite complex and
variable from place to place. Thus, preparing for tsunami strikes, and mitigating
their effects is not a simple process. And, of course, we cannot predict when an
earthquake will take place, and thus when a tsunami might occur, where that tsunami will make landfall, and what its size and impact might be.
While writing this chapter in fall 2018, a large earthquake occurred again in
Indonesia, but this time off Sulawesi (M w 7.5). It was not associated with a subduction zone (this could be a transform fault tsunami), but it was, once more, devastating (over 2000 dead). The systems that originally sent a tsunami warning were
canceled, but the tsunami made landfall just 30 min later…obviously something
went wrong. The funnel-shape of the coast caused the size of the tsunami to amplify
as it came shoreward (similar to how the Bay of Fundy works with tides – as the bay
narrows, the tidal amplitude increases…here, as the embayment at Palu narrowed,
the height of the tsunami waves increased). There will no doubt be considerable
scientific information to be gained from this event, but I’ll end by stating that it is
fundamentally important to transfer our scientific knowledge into informed preparation and mitigation plans and training so that coastal populations can react quickly
and appropriately when earthquakes (and potentially tsunami) occur.
Acknowledgments I would like to thank all those who mentored and participated in all of the
fieldwork I have had the pleasure of doing…it is absolutely the best part of the job of a coastal
geologist! I also acknowledge the Geological Society of America and National Science Foundation
for support. I look forward to the next adventure…there may be bears.
If You Would Like More Information
Atwater BF, Hemphill-Haley E (1997) Recurrence intervals for great earthquakes of the past 3,500
years at northeastern Willapa Bay, Washington, US Geological Survey Professional Paper
1576. US Geological Survey, Washington, DC
Cole SC, Atwater BF, McCutcheon PT, Stein JK, Hemphill-Haley E (1996) Earthquakeinduced burial of archaeological sites along the southern Washington coast about A.D. 1700.
Geoarchaeology 11:165–177
Hawkes AD, Horton BP, Nelson AR, Sawai Y, Vane CH (2011) Coastal subsidence in Oregon,
USA, during the giant Cascadia earthquake of AD 1700. Quat Sci Rev 30:364–376
Kelsey HM, Engelhart SE, Pilarczyk J, Horton BP et al (2015) Accommodation space, relative sea
level, and the archiving of paleo-earthquakes along subduction zones. Geology 43:675–678
A. D. Hawkes
land sediment, and forams are marine organisms), or they contained forams that
indicated brackish, intertidal environments. The tsunami sediments contained
forams from near-shore and deeper offshore marine environments. They provided
evidence of varying depths of excavation by tsunami waves offshore but also evidence of backwash tsunami flow – mangrove swamp forams that were deposited
seaward during the backwash. What was evident was that, by only using sediment
characteristics or only foraminiferal assemblages, we would not have gotten the full
picture. Both kinds of data together provide the best way to characterize tsunami
deposits, which you can see from my description here can be quite complex and
variable from place to place. Thus, preparing for tsunami strikes, and mitigating
their effects is not a simple process. And, of course, we cannot predict when an
earthquake will take place, and thus when a tsunami might occur, where that tsunami will make landfall, and what its size and impact might be.
While writing this chapter in fall 2018, a large earthquake occurred again in
Indonesia, but this time off Sulawesi (M w 7.5). It was not associated with a subduction zone (this could be a transform fault tsunami), but it was, once more, devastating (over 2000 dead). The systems that originally sent a tsunami warning were
canceled, but the tsunami made landfall just 30 min later…obviously something
went wrong. The funnel-shape of the coast caused the size of the tsunami to amplify
as it came shoreward (similar to how the Bay of Fundy works with tides – as the bay
narrows, the tidal amplitude increases…here, as the embayment at Palu narrowed,
the height of the tsunami waves increased). There will no doubt be considerable
scientific information to be gained from this event, but I’ll end by stating that it is
fundamentally important to transfer our scientific knowledge into informed preparation and mitigation plans and training so that coastal populations can react quickly
and appropriately when earthquakes (and potentially tsunami) occur.
Acknowledgments I would like to thank all those who mentored and participated in all of the
fieldwork I have had the pleasure of doing…it is absolutely the best part of the job of a coastal
geologist! I also acknowledge the Geological Society of America and National Science Foundation
for support. I look forward to the next adventure…there may be bears.
If You Would Like More Information
Atwater BF, Hemphill-Haley E (1997) Recurrence intervals for great earthquakes of the past 3,500
years at northeastern Willapa Bay, Washington, US Geological Survey Professional Paper
1576. US Geological Survey, Washington, DC
Cole SC, Atwater BF, McCutcheon PT, Stein JK, Hemphill-Haley E (1996) Earthquakeinduced burial of archaeological sites along the southern Washington coast about A.D. 1700.
Geoarchaeology 11:165–177
Hawkes AD, Horton BP, Nelson AR, Sawai Y, Vane CH (2011) Coastal subsidence in Oregon,
USA, during the giant Cascadia earthquake of AD 1700. Quat Sci Rev 30:364–376
Kelsey HM, Engelhart SE, Pilarczyk J, Horton BP et al (2015) Accommodation space, relative sea
level, and the archiving of paleo-earthquakes along subduction zones. Geology 43:675–678
A. D. Hawkes