David J. A. Barrell

High-frequency Holocene glacier fluctuations in New Zealand differ from the northern signature.

Vive La Différence How closely do climate changes in the Northern and Southern Hemispheres resemble each other? Much discussion has concentrated on the Holocene, the warm period of the past 11,500 years in which we now live, which represents a baseline to which contemporary climate change can be compared. Schaefer et al. (p. 622; see the Perspective by Balco) present a chronology of glacial movement over the last 7000 years in New Zealand, which they compare to similar records from the Northern Hemisphere. Clear differences are observed between the histories of glaciers in the opposing hemispheres, which may be owing to regional controls. Thus, neither of two popular arguments—that the hemispheres change in-phase or that they change in an anti-phased manner—appear to be correct. The patterns of glacial advances and retreats in New Zealand during the Holocene contrast markedly with those of the Northern Hemisphere. Understanding the timings of interhemispheric climate changes during the Holocene, along with their causes, remains a major problem of climate science. Here, we present a high-resolution 10Be chronology of glacier fluctuations in New Zealand’s Southern Alps over the past 7000 years, including at least five events during the last millennium. The extents of glacier advances decreased from the middle to the late Holocene, in contrast with the Northern Hemisphere pattern. Several glacier advances occurred in New Zealand during classic northern warm periods. These findings point to the importance of regional driving and/or amplifying mechanisms. We suggest that atmospheric circulation changes in the southwest Pacific were one important factor in forcing high-frequency Holocene glacier fluctuations in New Zealand.

Near-Synchronous Interhemispheric Termination of the Last Glacial Maximum in Mid-Latitudes

Isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation. However, 10Be exposure dates show that large-scale retreat of mid-latitude Last Glacial Maximum glaciers commenced at about the same time in both hemispheres. The timing of retreat is consistent with the onset of temperature and atmospheric CO2 increases in Antarctic ice cores. We suggest that a global trend of rising summer temperatures at the end of the Last Glacial Maximum was obscured in North Atlantic regions by hypercold winters associated with unusually extensive winter sea ice.

Complex multifault rupture during the 2016 Mw 7.8 Kaikōura earthquake, New Zealand

An earthquake with a dozen faults The 2016 moment magnitude (Mw) 7.8 Kaikōura earthquake was one of the largest ever to hit New Zealand. Hamling et al. show with a new slip model that it was an incredibly complex event. Unlike most earthquakes, multiple faults ruptured to generate the ground shaking. A remarkable 12 faults ruptured overall, with the rupture jumping between faults located up to 15 km away from each other. The earthquake should motivate rethinking of certain seismic hazard models, which do not presently allow for this unusual complex rupture pattern. Science, this issue p. eaam7194 At least 12 faults spaced up to 15 kilometers apart ruptured during the magnitude 7.8 Kaikōura earthquake. INTRODUCTION On 14 November 2016 (local time), northeastern South Island of New Zealand was struck by a major moment magnitude (Mw) 7.8 earthquake. The Kaikōura earthquake was the most powerful experienced in the region in more than 150 years. The whole of New Zealand reported shaking, with widespread damage across much of northern South Island and in the capital city, Wellington. The earthquake straddled two distinct seismotectonic domains, breaking multiple faults in the contractional North Canterbury fault zone and the dominantly strike-slip Marlborough fault system. RATIONALE Earthquakes are conceptually thought to occur along a single fault. Although this is often the case, the need to account for multiple segment ruptures challenges seismic hazard assessments and potential maximum earthquake magnitudes. Field observations from many past earthquakes and numerical models suggest that a rupture will halt if it has to step over a distance as small as 5 km to continue on a different fault. The Kaikōura earthquake’s complexity defies many conventional assumptions about the degree to which earthquake ruptures are controlled by fault segmentation and provides additional motivation to rethink these issues in seismic hazard models. RESULTS Field observations, in conjunction with interferometric synthetic aperture radar (InSAR), Global Positioning System (GPS), and seismology data, reveal the Kaikōura earthquake to be one of the most complex earthquakes ever recorded with modern instrumental techniques. The rupture propagated northward for more than 170 km along both mapped and unmapped faults before continuing offshore at the island’s northeastern extent. A tsunami of up to 3 m in height was detected at Kaikōura and at three other tide gauges along the east coast of both the North and South Islands. Geodetic and geological field observations reveal surface ruptures along at least 12 major crustal faults and extensive uplift along much of the coastline. Surface displacements measured by GPS and satellite radar data show horizontal offsets of ~6 m. In addition, a fault-bounded block (the Papatea block) was uplifted by up to 8 m and translated south by 4 to 5 m. Modeling suggests that some of the faults slipped by more than 20 m, at depths of 10 to 15 km, with surface slip of ~10 m consistent with field observations of offset roads and fences. Although we can explain most of the deformation by crustal faulting alone, global moment tensors show a larger thrust component, indicating that the earthquake also involved some slip along the southern end of the Hikurangi subduction interface, which lies ~20 km beneath Kaikōura. Including this as a fault source in the inversion suggests that up to 4 m of predominantly reverse slip may have occurred on the subduction zone beneath the crustal faults, contributing ~10 to 30% of the total moment. CONCLUSION Although the unusual multifault rupture observed in the Kaikōura earthquake may be partly related to the geometrically complex nature of the faults in this region, this event emphasizes the importance of reevaluating how rupture scenarios are defined for seismic hazard models in plate boundary zones worldwide. Observed ground deformation from the 2016 Kaikōura, New Zealand, earthquake. (A and B) Photos showing the coastal uplift of 2 to 3 m associated with the Papatea block [labeled in (C)]. The inset in (A) shows an aerial view of New Zealand. Red lines denote the location of known active faults. The black box indicates the Marlborough fault system

Glacier retreat in New Zealand during the Younger Dryas stadial

Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions. The presence of the Younger Dryas stadial (∼12.9 to ∼11.7 kyr ago) is established throughout much of the Northern Hemisphere, but the global timing, nature and extent of the event are not well established. Evidence in mid to low latitudes of the Southern Hemisphere, in particular, has remained perplexing. The debate has in part focused on the behaviour of mountain glaciers in New Zealand, where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent. The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question, fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period. Here we show that New Zealand’s glaciers retreated after ∼13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent ∼1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision 10Be chronology and reconstruction of former ice extents and snow lines from well-preserved cirque moraines. Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric CO2. The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand’s cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times, in turn leading to increased upwelling and CO2 release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas.

Fault kinematics and surface deformation across a releasing bend during the 2010 MW 7.1 Darfield, New Zealand, earthquake revealed by differential LiDAR and cadastral surveying

Dextral slip at the western end of the east-west–striking Greendale fault during the 2010 M_W 7.1 Darfield earthquake transferred onto a northwest-trending segment, across an apparent transtensional zone, here named the Waterford releasing bend. We used detailed surface mapping, differential analysis of pre- and postearthquake light detection and ranging (LiDAR), and property boundary (cadastral) resurveying to produce high-resolution (centimeter-scale) estimates of coseismic ground-surface displacements across the Waterford releasing bend. Our results indicate that the change in orientation on the Greendale fault incorporates elements of a large-scale releasing bend (from the viewpoint of westward motion on the south side of the fault) as well as a smaller-scale restraining stepover (from the viewpoint of southeastward motion on the north side of the fault). These factors result in the Waterford releasing bend exhibiting a decrease in displacement to near zero at the change in strike, and the presence within the overall releasing bend of a nested, localized restraining stepover with contractional bulging. The exceptional detail of surface deformation and kinematics obtained from this contemporary surface-rupture event illustrates the value of multimethod investigations. Our data provide insights into strike-slip fault bend kinematics, and into the potentially subtle but important structures that may be present at bends on historic and prehistoric rupture traces.

The geology of Dunedin, New Zealand, and the management of geological hazards

Abstract The city of Dunedin is located on the remains of a Miocene volcanic eruptive centre, which is underlain by Tertiary marine sediments and Late Cretaceous quartz gravel, sand and clay with some coal seams. These in turn rest on a basement of Jurassic schist. The geology and topography pose a number of geological hazards that must be considered in urban development. These include landslide, mine subsidence, ground shaking amplification and liquefaction, coastal erosion and tsunami. A number of research, policy and planning initiatives have been undertaken to assess and mitigate the effects of these hazards. A GIS-based Hazard Information System (for a part of the city) was developed to assist in identifying and mitigating hazards. Under legislation the Dunedin City Council (DCC) is obliged to keep a register of known hazards. In addition, a Lifelines project has been undertaken to identify hazards and related risks to emergency and utility services. These studies may be used by asset managers to prioritise mitigation measures for critical facilities as well as to avoid hazards. The DCC district plan includes policies to gather and maintain hazard information, encourage research into hazards, and control activities in areas that might be affected by hazards.

Mismatch of glacier extent and summer insolation in Southern Hemisphere mid-latitudes

Here we address a long-standing puzzle of ice-age climate called the “fly in the ointment of the Milankovitch theory.” Using geomorphic mapping and 10Be surface-exposure dating, we show that five moraine belts were formed during maxima of the last ice age by the Pukaki glacier in New Zealand’s Southern Alps. They afford ages of 41.76 ± 1.09 ka, 35.50 ± 1.26 ka, 27.17 ± 0.68 ka, 20.27 ± 0.60 ka, and 18.29 ± 0.49 ka. These five maxima spanned an entire precessional cycle in summer insolation intensity at the latitude of the Southern Alps. A similar mismatch between summer insolation and glacier extent also characterized the Chilean Lake District in the mid-latitudes of South America. Thus, in apparent contrast to northern ice sheets linked by Milankovitch to summer insolation at 65°N latitude, the behavior of southern mid-latitude glaciers was not tied to local summer insolation intensity. Instead, glacier extent between 41.76 ka and 18.29 ka, as well as during the last termination, was aligned with Southern Ocean surface temperature and with atmospheric carbon dioxide.

Surface Rupture of Multiple Crustal Faults in the 2016 Mw 7.8 Kaikōura, New Zealand, Earthquake

Multiple (>20 >20 ) crustal faults ruptured to the ground surface and seafloor in the 14 November 2016 M w Mw 7.8 Kaikōura earthquake, and many have been documented in detail, providing an opportunity to understand the factors controlling multifault ruptures, including the role of the subduction interface. We present a summary of the surface ruptures, as well as previous knowledge including paleoseismic data, and use these data and a 3D geological model to calculate cumulative geological moment magnitudes (M G w MwG ) and seismic moments for comparison with those from geophysical datasets. The earthquake ruptured faults with a wide range of orientations, sense of movement, slip rates, and recurrence intervals, and crossed a tectonic domain boundary, the Hope fault. The maximum net surface displacement was ∼12  m ∼12  m on the Kekerengu and the Papatea faults, and average displacements for the major faults were 0.7–1.5 m south of the Hope fault, and 5.5–6.4 m to the north. M G w MwG using two different methods are M G w MwG 7.7 +0.3 −0.2 7.7−0.2+0.3 and the seismic moment is 33%–67% of geophysical datasets. However, these are minimum values and a best estimate M G w MwG incorporating probable larger slip at depth, a 20 km seismogenic depth, and likely listric geometry is M G w MwG 7.8±0.2 7.8±0.2 , suggests ≤32% ≤32% of the moment may be attributed to slip on the subduction interface and/or a midcrustal detachment. Likely factors contributing to multifault rupture in the Kaikōura earthquake include (1) the presence of the subduction interface, (2) physical linkages between faults, (3) rupture of geologically immature faults in the south, and (4) inherited geological structure. The estimated recurrence interval for the Kaikōura earthquake is ≥5,000–10,000  yrs ≥5,000–10,000  yrs , and so it is a relatively rare event. Nevertheless, these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries.

A 3D Geological Model for Christchurch City (New Zealand): A Contribution to the Post-earthquake Re-build

Geological maps for areas of high density population play an important role in the design and planning of building and network infrastructure as well as management of subsurface resource such as groundwater and aggregate. The Christchurch urban area, New Zealand, experienced high ground shaking accelerations during the 2010–2011 Canterbury earthquake sequence (CES) and the built environment suffered serious damage from shaking and consequent liquefaction. Damage from the earthquakes focused efforts to improve understanding of materials and their properties beneath that city. This paper presents a summary of work undertaken to build a high resolution 3D geological model of these materials, including geomorphological mapping and analysis of materials using a large number of drillhole logs and digital cone penetration tests. An integrated 3D geological model and 3D numerical geotechnical models will contribute to the re-building of Christchurch and its infrastructure following the destructive earthquakes. Potential uses include planning optimal routing for major horizontal infrastructure (sewer, drainage and water supplies) where some fore-knowledge of foundation conditions will allow re-alignment to easier substrates, more accurate cost estimates and more focused site specific foundation testing.

The deglaciation of Lake Pukaki, South Island, New Zealand—a review

The last major ice advance of the Pukaki Glacier and subsequent onset of retreat occurred at c. 18,000 cal yr BP, and c. 400 m of ice surface lowering occurred prior to 16,165 ± 887 cal yr BP. Sediments and landforms near the lake outlet indicate initial formation of the lake somewhere between c. 510 and 520 m above sea level (asl), with initial lacustrine deposition of ice-proximal well-bedded Fancy Sands and localised coarse angular gravel accumulations likely derived from melting icebergs. Rapid ice retreat formed a large lake, at least c. 30 km long, at c. 510 m asl, with lacustrine deposition near the outlet of silty clay (Pukaki Pug) which contains as much as 40% diatoms. An age of 13,492 ± 293 cal yr BP for a piece of wood from Pukaki Pug is a minimum for withdrawal of the Pukaki Glacier from the outlet area.