Environment Studies – Tsunami

Environment Studies – Tsunami
Q1. Present a short report on the effect of a tsunami coming ashore at the Carso in Manly. Descripe the physical effect on the Cargo for the three scenarios
1. A 5 M runup tsunami at high tide
2. A5 M runup at lower tide.
3. A12 M runup tsunami at high tide

Q2. under what condation wound damange at the Cargo be enhanced?Under what condation wound damage be minimised?
Practical 3 – Tsunami

Introduction
“Tsunami” are well known perils forming from sudden volumetric displacement of sea water through earthquake upheaval, shelf slump, edifice failure or cosmic impactor.

Energy in the form of long-wavelength waves radiates from the site of water displacement. These are known as “tsunami” (|(t)soo’näme|). I understand the origin of the word is from the combination of the Japanese words “tsu” (harbour) and “nami” (wave), after the propensity of these waves to manifest themselves strongly at harbours which typically lie at the heads of inlets.

Tsunami waves travel rapidly and efficiently over long distances, having ocean basin-wide and in some cases global effects. Waves from earthquakes and shelf slumps can have >30 m height runup at the shore and can be much larger for cosmic impactor waves.

Are Tsunami important for NSW?
There is no doubt that NSW (and NZ) have received tsunami; small ones historically and larger ones in the geological past (papers 1-3). However the sedimentological evidence for very large tsunami along the coast of NSW remains controversial (cf papers 4-6). Despite this uncertainty, most of Australia’s population is at the coast and many within a few metres of sea level (paper 7) and our vulnerability to tsunami appears to be high (papers 8-10).
Present a short (400 word max) report on the effects of a tsunami coming ashore at the Corso in Manly. Describe the physical effects on the Corso for three scenarios;
1. A 5 m runup tsunami at high tide,
2. A 5 m runup tsunami at low tide,
3. A 12 m runup tsunami at high tide.

4. Under what conditions would damage be enhanced? Under what conditions would damage be minimised?

Helpful hints
If you have never been to the Corso at Manly, use Google Maps and StreetView to help. Go to;
https://maps.google.com.au/maps?hl=en
Enter “The Corso, Manly, NSW” into the address box.
Use StreetView to help you. See a small yellow person at the “+” sign on the zoom slider on top left of the image? Drag that person onto the Corso and you will then be able to navigate around the Corso at Street Level. Make sure you look at the distribution (where it is, plus how high it is) of people/items/investments and consider how vulnerable each might be to tsunami.
Reading

The reading list below is not exhaustive by any means; it is a selection from (mostly) recent published papers. You may choose to understand tsunami from the perspectives of other authors either as well as, or instead of, the ones below.

1. Dominey-Howes, D. 2007. Marine Geology 239(1-2), 99-123.

The Indian Ocean tsunami (IOT) of 2004 has resulted in significant interest within Australia about the record of tsunami for the continent because an understanding of tsunami hazard begins with a catalogue of past events. Here, a preliminary catalogue of tsunami affecting Australia is presented. The catalogue contains entries for 57 tsunami events. The oldest event is dated at 3.47 Ga, the most recent is the July 17th 2006. Forty-four tsunami were recorded on the New South Wales coast although the NW coast of Western Australia records a significant number of events. Forty-seven events have affected Australia since AD1858. Maximum run-up for an historic event is + 6 m asl whilst the maximum run-up for a palaeotsunami event is reported at an elevation of at least + 100 m asl. Twenty-three percent of historic Australian tsunami were generated by unknown causes and Papua New Guinea, the Solomon Islands and Indonesia collectively represent the most important source area of historic tsunami for Australia. Geological records for palaeo and historic tsunami are identified and summarised. The geological record of tsunami represents a potentially important source of information for Australian tsunami. However, at the present time, the geological record is both limited and controversial and future research should seek to re-examine proposed geological evidence of tsunami. From an analysis of this preliminary catalogue of Australian tsunami, a series of key research priorities have been identified to guide future research in the region.
2. Goff, J. et al. 2010. Development of a palaeotsunami database for New Zealand. Natural Hazards 54(2), 193-208.

A New Zealand palaeotsunami database has been developed. The philosophy has been to include as much tsunami-related data as possible. Most of the events recorded are true palaeotsunamis that occurred prior to the historical record or have no written observations. Some are hybrids that are in some manner poorly recorded historical events. Data include physical evidence from geological, archaeological and geomorphological sources and cultural information from anthropological research and prehistorical Maori oral recordings. Each line of data represents a summary of one piece of evidence containing key details listed under a series of headings. The estimated veracity of each line item is based upon the sum of the information contained in the linked reference(s). The palaeotsunami database contains approximately 300 line items and describes between 35 and 40 palaeotsunamis. This wealth of data helps to improve our understanding of tsunami sources, event its magnitude and frequency.
3. Young, R.W. et al. 1997. Chronology of Holocene tsunamis on the southeastern coast of Australia. Transactions – Japanese Geomorphological Union 18(1), 1-19.

A chronology is outlined based on 22 C14 ages and 23 TL (thermoluminescence) ages from sites along 400 km of coast. At least five, and probably six major tsunamis struck this coast during the Holocene. These events occurred at about 250, 500-800, 1600-1900, 3000, 6500 and 8700-9000 years ago. The frequency of these events was about 1 in 1300 years over the whole Holocene, but increased to about 1 in 600 years during the last 3000 years. This is the same frequency as the tectonically active Ryukyu Islands.
4. Bryant, E.A. et al. 1996. Tsunami as a major control on coastal evolution, southeastern Australia. Journal of Coastal Research 12(4), 831-840.

General concepts of coastal evolution of the southeastern Australian coastline during the Late Pleistocene involve barrier formation by wind and swell waves during marine transgressions and formation of rock platforms by chemical and mechanical weathering at rates of 1-5 mm yr-1. Where evidence indicates rapid change, storms are often invoked as the causative mechanism. These concepts ignore the important role of a repetitive, rapid, catastrophic tsunami in both coastal erosion and accretion. The impact of a tsunami can be distinguished by four signatures: uncemented clastic deposits; boulders that are imbricated, stacked and uniformly aligned; constructional features; and erosional bedrock sculpturing. The boulder deposits occur at elevations above both the measured and theorised limits of storm-wave action. Bedrock sculpturing has not been attributed previously to marine processes but rather to catastrophic water flow from icesheets or ice-dammed lakes, a phenomenon which has never influenced the mainland coast of Australia during the Pleistocene. Thermoluminescence dating has shown that tsunamis in southeastern Australia, while eroding most Last Interglacial and interstadial barriers, have also contributed to the construction of many present barriers. They have also shaped the rocky coast by modifying raised platforms and in extreme cases ripping enormous slabs of bedrock from promontories and cliff faces up to heights of 40-50 m. A change in emphasis in the current thinking regarding the processes responsible for coastal evolution is needed in coastal geomorphology to include the impact of repetitive tsunamis which are capable of dramatically and irrevocably modifying a landscape over very short periods of time.
5. Young, R.W. et al. 1996. Catastrophic wave (tsunami?) transport of boulders in southern New South Wales, Australia. Zeitschrift für Geomorphologie 40(2), 191-207.

Deposits of large boulders above modern limits of storm waves along the coast of southern New South Wales record catastrophic wave action. The largest boulders that were moved weigh 80-90 tonnes, and the maximum height of wave action was 32 m. Hydraulic reconstruction indicates flow depths of 3.4 and perhaps > 4 m and velocities of 5.5 m/s to 10.3 m/s. Cavitation features on some rock surfaces support the estimates of maximum velocities. A remarkably limited range in the orientation of imbricated boulders along 150 km indicates that the deposits record a single event that approached from the SE. to SSE. The fabric and size of the deposits point to a tsunami wave train rather than to exceptional storm waves. The most probable source of the wave train is the Macquaric Ridge in the south Tasman Sea. An earliest Holocene age for the event is indicated by a thermoluminescence determination of 9.5ka from sand associated with one boulder deposit, and by the transport of some boulders from below present sea level.
6. Goff, J. et al. 2010. Testing the hypothesis for tsunami boulder deposition fom suspension. Marine Geology 277(1-4), 73-77.

Tsunamis are known to deposit boulders but it is not clear if they are transported solely as bed load or whether suspended load can be involved. It has been reported that numerous individual boulders and imbricated boulder stacks at elevations above normal storm tide levels along the New South Wales (NSW) coast of SE Australia, have been deposited out of suspension by tsunamis. The NSW coast therefore provides an important natural laboratory to test the hypothesis that tsunamis can deposit large boulders from suspension. Using standard hydrodynamic equations to formulate the relationship between boulder transport and flow depth, we provide a test of the suspension hypothesis. We show that the tsunami flow depths required for deposition from suspension are most probably physically unrealistic. The NSW boulders are therefore not indicative of deposition from suspension and an alternative explanation must be sought for their mechanism of emplacement. This analysis has important implications for the emerging sub-branch of tsunami boulder geology.
7. Chen, K. & McAneney, J. 2006. High-resolution estimates of Australia’s coastal population. Geophysical Research Letters 33(16), L16601

Here we quantify Australian coastal population at a spatial resolution of 1 km and do this as a function of distance to shoreline and elevation above mean sea level. We also report comprehensive validations based on statistical and spatial relationships between very fine-resolution Australian data sets and the recent high-resolution global data sets on ambient population distribution (LandScan2003), shorelines (GSHHS) and elevation (SRTM). Estimates are heavily dependent upon the resolutions of all input data, as well as the resolution of analysis. Our results show about 50% of Australian addresses or population are located within 7 km of the shore, and that population decreases very rapidly with increasing distance from the shoreline. About 6.0% of Australian addresses are situated within 3 km of shorelines in areas with elevations below 5 m.

8. Dall’Osso, F. & Dominey-Howes, D. 2010. Public assessment of the usefulness of “draft” tsunami evacuation maps from Sydney, Australia -implications for the establishment of formal evacuation plans. Natural Hazards and Earth System Science 10(8), 1739-1750.

Australia is at risk from tsunamis and recent work has identified the need for models to assess the vulnerability of exposed coastal areas -a fundamental element of the risk management process. Outputs of vulnerability assessment can be used as a baseline for the generation of tsunami prevention and mitigation measures, including evacuation maps. Having noted that no evacuation maps exist for Manly, Sydney (an area recently subjected to high resolution building vulnerability assessment by Dall’Osso et al., 2009b), we use the results of the analysis by Dall’Osso et al. (2009b) to “draft” tsunami evacuation maps that could be used by the local emergency service organisations. We then interviewed 500 permanent residents of Manly in order to gain a rapid assessment on their views about the potential usefulness of the draft evacuation maps we generated. Results of the survey indicate that residents think the maps are useful and understandable, and include insights that should be considered by local government planners and emergency risk management specialists during the development of official evacuation maps (and plans) in the future.
9. Dall’Osso, F. et al. 2009. A revised (PTVA) model for assessing the Vulnerability of buildings to Tsunami damage. Natural Hazards and Earth System Science 9(5), 1557-1565.

The Papathoma Tsunami Vulnerability Assessment (PTVA) Model (Papathoma, 2003) was developed in the absence of robust, well-constructed and validated building fragility models for assessing the vulnerability of buildings to tsunami. It has proven to be a useful tool for providing assessments of building vulnerability. We present an enhanced version (PTVA-3) of the model that takes account of new understanding of the factors that influence building vulnerability and significantly, introduce the use of the Analytic Hierarchy Process (AHP) for weighting the various attributes in order to limit concerns about subjective ranking of attributes in the original model. We successfully test PTVA- 3 using building data from Maroubra, Sydney, Australia.
10. Dall’Osso, F. et al. 2009. Assessing the vulnerability of buildings to tsunami in Sydney. Natural Hazards and Earth System Science 9(6), 2015-2026.

Australia is vulnerable to the impacts of tsunamis and exposure along the SE coast of New South Wales is especially high. Significantly, this is the same area reported to have been affected by repeated large magnitude tsunamis during the Holocene. Efforts are under way to complete probabilistic risk assessments for the region but local government planners and emergency risk managers need information now about building vulnerability in order to develop appropriate risk management strategies. We use the newly revised PTVA-3 Model (Dall’Osso et al., 2009) to assess the relative vulnerability of buildings to damage from a “worst case tsunami” defined by our latest understanding of regional risk – something never before undertaken in Australia. We present selected results from an investigation of building vulnerability within the local government area of Manly – an iconic coastal area of Sydney. We show that a significant proportion of buildings (in particular, residential structures) are classified as having “High” and “Very High” Relative Vulnerability Index scores. Furthermore, other important buildings (e.g., schools, nursing homes and transport structures) are also vulnerable to damage. Our results have serious implications for immediate emergency risk management, longer-term land-use zoning and development, and building design and construction standards. Based on the work undertaken here, we recommend further detailed assessment of the vulnerability of coastal buildings in at risk areas, development of appropriate risk management strategies and a detailed program of community engagement to increase overall resilience.
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