The enigma of intricately fitted beach boulders near Raglan, New Zealand

Nelson, C. H.; Hood, Sean

doi:10.1080/00288306.2016.1168456

Cited by 2 publications

(1 citation statement)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The greater number of CSBs favoured an in‐depth study of alignment patterns. In coastal locations with a high rate of boulder supply, it is reasonable to expect boulders to become “fitted” over time by a combination of weathering processes, wave microvibration, and/or mechanical abrasion (Hills, ; Nelson & Hood, ; Shelley, ). The geomorphic process of fitting refers to adjacent clasts becoming tightly packed in a three‐dimensional interlocking mass, affording considerable stability.…”

Section: Discussionmentioning

confidence: 99%

Strongly aligned coastal boulders on Ko Larn island (Thailand): a proxy for past typhoon‐driven high‐energy wave events in the Bay of Bangkok

Terry

Goff

2019

Geographical Research

View full text Add to dashboard Cite

Recent studies of elevated carbonate boulder deposits on several rock islands near Bangkok have indicated that Thailand's capital city may not be as protected from typhoon strikes as previously thought. Here, new evidence is presented for past high‐energy wave (HEW) events in the form of statistically significant patterns of boulder alignment on exposed rocky shorelines of Ko Larn island. The long‐axis orientations of 193 coastal sandstone boulders were analysed across four study sites. Several scenarios for the unimodal, bimodal, and polymodal patterns found can be envisaged. Either the most recent HEW event was the strongest—in which case most clasts were rearranged unimodally (one observation site), or the strongest HEW event was earlier and subsequent weaker ones realigned only smaller boulders to produce bimodal or polymodal patterns (three observation sites). Inferred northeastward or eastward onshore flow directions are consistent with palaeo‐typhoons penetrating into the Bay of Bangkok on northwestward curving tracks. The calculated minimum flow velocities required to transport all sampled boulders are 5.5–7.8 m s−1, similar to other findings throughout the Asia‐Pacific region. It was observed that the absence of a fitted boulder geomorphology lends credence to the earlier proposed time frame of 150–200 years between typhoon phases in the upper Gulf of Thailand. The current work has provided additional insights into the characteristics of past HEW events that have a possibility of reoccurring again at some time in the future. Our findings continue to raise awareness for a reassessment of the risks of coastal hazards for the Chao Phraya River delta and densely populated Bangkok, for which storm surge modelling should be an urgent priority, so as to give better perceptions on how typhoon‐driven marine incursion would impact the city.

show abstract

Section: Discussionmentioning

confidence: 99%

Strongly aligned coastal boulders on Ko Larn island (Thailand): a proxy for past typhoon‐driven high‐energy wave events in the Bay of Bangkok

Terry

Goff

2019

Geographical Research

View full text Add to dashboard Cite

show abstract

Engineering geomorphology of coastal landslides at Limestone Downs, North Island, New Zealand

Mueller,

Simmons,

Brook

2024

QJEGH

View full text Add to dashboard Cite

Coastal landslides are widespread geomorphological features on New Zealand's North Island, representing a key coastal erosion process. Often, New Zealand's coastal landsliding is rainfall-induced, with young, weak, permeable sediments, failing along a shear surface coincident with an unconformable contact with underlying older, sedimentary rock. An example is the Plio-Pleistocene Awhitu Group sands in the west of the North Island, which in recent years have failed via extremely rapid flows, with little warning, leading to fatalities at built-up coastlines. Understanding the nature of the hazard posed by coastal landslides is often precluded by the heavily vegetated nature of the coast, and site access. We present a case study of two coastal landslides at Limestone Downs, on the Waikato coast, ∼70 km south of Auckland, using field investigation, laboratory testing, remote sensing and modeling. The northern landslide appears to be a relict, low-angle bedding-plane failure in sedimentary rock, possibly between the Miocene Waikawau Sandstone and the underlying Te Kuiti Group. In contrast, the adjacent southern landslide appears active, failing by retrogressive upslope extension, and is limited to Plio-Pleistocene Awhitu Group sediments. While both landslides may have been initiated by marine erosion, triggering from near-field earthquakes and tsunami effects cannot be ruled out.

show abstract

The enigma of intricately fitted beach boulders near Raglan, New Zealand

Cited by 2 publications

References 28 publications

Strongly aligned coastal boulders on Ko Larn island (Thailand): a proxy for past typhoon‐driven high‐energy wave events in the Bay of Bangkok

Strongly aligned coastal boulders on Ko Larn island (Thailand): a proxy for past typhoon‐driven high‐energy wave events in the Bay of Bangkok

Engineering geomorphology of coastal landslides at Limestone Downs, North Island, New Zealand

Contact Info

Product

Resources

About