Discovery of halloysite books in a ~270,000 year-old buried tephra deposit in northern New Zealand

As part of a wider study examining the geomechanical properties, especially sensitivity, of sequences of Quaternary pyroclastic and associated deposits and buried soils in the landslide-prone western Bay of Plenty area near Tauranga, eastern North Island, we examined the mineralogy of a pale pinkish-grey tephra deposit directly beneath non-welded, siliceous Te Ranga Ignimbrite (~2 m thick) in a ~25 m high cutting at Tauriko.http://www.smectech.com.au/ACMS/ACMS_Conferences/ACMS21/ACMS%202010%20Abstracts/ACMS%202010%20S1A6_Wyatt%20et%20al%20(Lowe).pd

Landslides in sensitive soils, Tauranga, New Zealand.

In the Tauranga region sensitive soil failures commonly occur after heavy rainfall events, causing considerable infrastructure damage. Several notable landslides include a large failure at Bramley Drive, Omokoroa in 1979, the Ruahihi Canal collapse in 1981, and numerous landslides in May 2005; recently the Bramley Drive scarp was reactivated in 2011. These failures are associated with materials loosely classified as the Pahoia Tephras - a mixture of rhyolitic pyroclastic deposits of approximately 1 Ma. The common link with extreme rainfall events suggests a pore water pressure control on the initiation of these failures. Recent research on the structure of the soils shows a dominance of halloysite clay minerals packed loosely in arrangements with high porosity (51 – 77 %), but with almost entirely micropores. This leads us to conclude that the permeability is very low, and the materials remain continuously wet. The formation of halloysite is encouraged by a wet environment with no episodes of drying, supporting this assumption. A high-resolution CPT trace at Bramley Drive indicates induced pore water pressures rising steadily to a peak at approximately 25 m depth; this depth coincides with the base of the landslide scarp. We infer that elevated pore water pressures develop within this single, thick aquifer, triggering failure through reduced effective stresses. The inactive halloysite clay mineral results in low plasticity indices (13 – 44 %) and hence high liquidity indices (1.2 – 2.4) due to the saturated pore space; remoulding following failure is sudden and dramatic and results in large debris runout distances

Discovery of halloysite books in altered silicic Quaternary tephras, northern New Zealand

Hydrated halloysite was discovered in books, a morphology previously associated exclusively with kaolinite. From ~1.5 μm to ~1500 μm in length, the books showed significantly greater mean Fe contents (Fe2O3 = 5.2 wt%) than tubes (Fe2O3 = 3.2 wt%), and expanded rapidly with formamide. They occurred, along with halloysite tubes, spheroids, and plates, in highly porous yet poorly-permeable, silt-dominated, Si-rich, pumiceous rhyolitic tephra deposits aged ~0.93 Ma (Te Puna tephra) and ~0.27 Ma (Te Ranga tephra) at three sites ~10-20 m stratigraphically below the modern land-surface in the Tauranga area, eastern North Island, New Zealand. The book-bearing tephras were at or near saturation, but have experienced intermittent partial drying, favouring the proposed changes: solubilized volcanic glass + plagioclase -> halloysite spheroids -> halloysite tubes -> halloysite plates -> halloysite books. Unlike parallel studies elsewhere involving both halloysite and kaolinite, kaolinite has not formed in Tauranga presumably because the low permeability ensures the sites largely remain locally wet so that the halloysite books are metastable. An implication of the discovery is that some halloysite books in similar settings may have been misidentified previously as kaolinite

The environment of high-mass star formation: A study of the molecular environment within two giant molecular clouds

If a giant molecular cloud (GMC) begins with the same molecular abundances throughout, then any changes observed between different clumps within that GMC are due to its evolutionary stage. By studying how high-mass stars form from clumps, we are able to identify how they shape and are shaped by their environment. We study two different GMCs: the G333 GMC and cloud C of the Vela Molecular Ridge (VMR-C). For the G333 GMC, we enhanced a 3-mm molecular line survey conducted on the Mopra radio telescope by including ammonia (temperature) observations targeted towards dust clumps with the Tidbinbilla 70-m radio telescope. For the VMR-C GMC, we conducted a 12-mm molecular line survey on the Mopra radio telescope. We detected emission for ammonia, cyanoacetylene, cyanobutadiynene, and the water maser line. We modelled the spectral energy distribution for the five dust clumps identified by the water maser emission. We studied the morphology and turbulent properties of both GMCs using molecular transitions from carbon monoxide and its isotopologues, hydrogen cyanide, hydrogen isocyanide, formylium, and diazenylium. In G333 GMC, we find evidence that the clumps identified by molecular emission are substantial in size. Clumps with star formation signs are generally warmer and have larger turbulent line widths. We find evidence of radially triggered star formation in the G333 GMC: infrared clumps without obvious signs of star formation are found preferentially further away from known sites of star formation. We highlight the differences between star formation in the two GMCs by analysing the probability distribution function (PDF) of the molecular gas. Both GMCs have a hierarchical, turbulence driven component, and a gravitationally bound component; with less gravitationally bound gas in the VMR-C GMC. We trialled a new technique: the PDF analysis of molecular lines and show that it can identify real differences between molecular clouds

MALT-45: a 7 mm survey of the southern Galaxy - I. Techniques and spectral line data

We present the first results from the MALT-45 (Millimetre Astronomer's Legacy Team-45 GHz) Galactic Plane survey. We have observed 5 square degrees (l = 330°–335°, b = ±0 ∘ . 5) for spectral lines in the 7 mm band (42–44 and 48–49 GHz), including CS (1–0), class I CH3OH masers in the 7(0,7)–6(1,6) A+ transition and SiO (1–0) v = 0, 1, 2, 3. MALT-45 is the first unbiased, large-scale, sensitive spectral line survey in this frequency range. In this paper, we present data from the survey as well as a few intriguing results; rigorous analyses of these science cases are reserved for future publications. Across the survey region, we detected 77 class I CH3OH masers, of which 58 are new detections, along with many sites of thermal and maser SiO emission and thermal CS. We found that 35 class I CH3OH masers were associated with the published locations of class II CH3OH, H2O and OH masers but 42 have no known masers within 60 arcsec. We compared the MALT-45 CS with NH3 (1,1) to reveal regions of CS depletion and high opacity, as well as evolved star-forming regions with a high ratio of CS to NH3. All SiO masers are new detections, and appear to be associated with evolved stars from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Generally, within SiO regions of multiple vibrational modes, the intensity decreases as v = 1, 2, 3, but there are a few exceptions where v = 2 is stronger than v = 1

Evaluating soil and landscape models to predict liquefaction susceptibility in the Hinuera Formation, Hamilton Basin

Cone Penetration Tests (CPT) derived from the Hamilton section of the Waikato Expressway were analysed within CLiqTM software. The derived Liquefaction Potential Index (LPI) from each CPT was then combined with LIDAR, pedological and geological maps for statistical analysis. A soil model that incorporates the conditions of modern soil development with these derived LPI values was developed as a preliminary assessment tool for liquefaction potential within Hamilton Basin soils. The model shows that liquefaction is more likely to occur on interfluvial areas where there is little topographical relief. Pedological soils with high organic component are also a likely indicator of high liquefaction susceptibility

Soil recovery following landsliding at Whatawhata Research Station, Waikato, New Zealand: preliminary results

This research investigates soil recovery following landslides at the Whatawhata Research Station 20 km west of Hamilton. Six landslides were studied, ranging in age from pre-1953 to 2014. The landslides were divided into four zones: shear zones (mean of 25% of landslide area), intact accumulation zones (20%), transition zones (40%), and re-deposition zones (15%), along with a control. Soils were well developed in the control and intact accumulation zones and least recovered in the shear and re-deposition zones. Mean A horizon depths ranged from 2 cm in the shear and re-deposition zones to 7 cm in the transition zone, 17 cm in the intact accumulation zone, and 20 cm in the control. Mean soil carbon contents were lower (P<0.05) in the landslide zones (range of 3.2-5.2%) than in the controls (8.2%). Older landslides showed great recovery; however, the differences between zones within the landslides were greater than the differences between landslides

Paleoliquefaction in Late Pleistocene alluvial sediments in Hauraki and Hamilton basins, and implications for paleoseismicity

Liquefaction susceptibility of the Late Pleistocene Hinuera Formation is of interest to the engineering community as it is unclear whether materials of this age will still be prone to activation by cyclic stresses. In this paper we report on rare paleoliquefaction features in the form of injection structures that we have identified at two sites near Hamilton. These structures are clearly earthquake induced, and indicate the potential for future liquefaction episodes. However, we suggest that the hazard is restricted to areas with impeded drainage that imparts a high water table. Such areas are localised, and may be recognised from the modern (pedological) soil distribution. Evaluating piezocone penetration test (CPTu) data from the sites of known paleoliquefaction indicates that the CPTu gives a meaningful indication of liquefaction potential, and questions the validity of applying aging factors to these deposits

Rainfall threshold for initiating effective stress decrease and failure in weathered tephra slopes

Rainfall is one of the most important triggers of slope failure. Weathered pyroclastic (tephra) deposits are especially vulnerable to slope failure because they commonly form slopes of high porosity and high clay content. Empirically derived thresholds for the triggering of landslides are commonly based on rainfall conditions and have been widely applied in volcanic soils. However, so far only few researchers utilized pore water pressure in the slope as additional variable for the threshold calibration. Here, we derived a new rainfall threshold for initiating the decrease in effective stress in the slope by analyzing a long-term record of rainfall and piezometer data from a slide-prone coastal area in northern New Zealand that consists of clayey, halloysitic tephra deposits. The level of effective stress decrease increased with rainfall intensity and duration. We observed highest effective stress decrease of up to 36% during rainfall events that triggered landslides in our study area. The effective stress threshold exhibits a satisfactory predictive capability. The probability of correctly predicting a decrease in effective stress is 53%. The effective stress threshold contributes towards the implementation of the decrease in effective stress into rainfall thresholds for the occurrence of landslides