title: Rheology and Flow Emplacement Processes of the 1954 Lavas, Mount Ngauruhoe

authors: Sanders, Fiona

subjects: Ngauruhoe

abstract: The rheology and emplacement dynamics of basaltic and rhyolitic lava flows have been studied extensively, leading to the development of numerous rheological and flow behaviour models; however, the flow dynamics of more intermediate composition lavas, particularly those emplaced on relatively steep slopes, is less well-constrained. The 1954-55 eruption of Mount Ngauruhoe, a young, composite cone of the Tongariro Volcanic Centre, generated at least 11, well-preserved, spatter-fed, basaltic andesite a'a lavas on the steep, north-west flanks of the cone. The rheological properties and flow dynamics of these lavas are quantified by incorporating morphological, petrographic and geochemical data collected from these flow deposits into a range of existing numerical models, and the results compared with documented eye-witness accounts. 

The lava flow deposits are typically long, narrow, discrete units characterised by comparable morphological traits on the steep slopes of the cone and varying in dimension, morphology and flow surface features on the shallower slopes. Flow surfaces are typically autobrecciated and display a large-scale, lateral trend in clast size and morphology across flow widths. The 1954 lavas are petrographically and geochemically homogenous with no apparent trends associated with successively emplaced lava flows. The rheological properties of the lavas at the time of initial flow advance are therefore assumed to be comparable for each flow. Lava viscosity was estimated at 102 to 104 Pa s for the temperature range 1150 to 950 C. Yield strength was difficult to quantify but is assumed in this study to be relatively low (~ 25 Pa). Calculated flow velocity, effusion rate and emplacement duration are not well-constrained against documented eye-witness accounts. Mean flow velocity (0.03 to 0.04 m/s) was estimated from eye-witness reports, and used to determine flow emplacement durations between ~ 2 to 48 hours, comparable with documented duration times. Effusion rates could not be definitively quantified but flow deposit morphology and documented accounts indicate that intermittent episodes of high effusion rates over a short duration were associated with the emplacement of the 1954 lavas. 

Three major controls on the emplacement of the 1954 lava flows have been identified. Effusion rate and duration was the primary control on the development of single unit lava flows, flow channel drainage on steep slopes and in limiting run-out distances from the vent. Low initial viscosity and yield strength promoted high flow velocities on steep slopes and low surface cooling rates. Relatively short flow emplacement duration times precluded significant downflow viscosity and yield strength increases. Slope gradient and topographic obstacles were major controls on flow emplacement processes. Slope gradient was the dominant control on flow velocity, flow width and depth and surface autobrecciation, while morphology, flow path direction and surface folding were constrained by local slope gradient variations and/or topographic obstacles.

text: Rheology and Flow Emplacement Processes of the 1954 Lavas, Mount Ngauruhoe The rheology and emplacement dynamics of basaltic and rhyolitic lava flows have been studied extensively, leading to the development of numerous rheological and flow behaviour models; however, the flow dynamics of more intermediate composition lavas, particularly those emplaced on relatively steep slopes, is less well-constrained. The 1954-55 eruption of Mount Ngauruhoe, a young, composite cone of the Tongariro Volcanic Centre, generated at least 11, well-preserved, spatter-fed, basaltic andesite a'a lavas on the steep, north-west flanks of the cone. The rheological properties and flow dynamics of these lavas are quantified by incorporating morphological, petrographic and geochemical data collected from these flow deposits into a range of existing numerical models, and the results compared with documented eye-witness accounts. 

The lava flow deposits are typically long, narrow, discrete units characterised by comparable morphological traits on the steep slopes of the cone and varying in dimension, morphology and flow surface features on the shallower slopes. Flow surfaces are typically autobrecciated and display a large-scale, lateral trend in clast size and morphology across flow widths. The 1954 lavas are petrographically and geochemically homogenous with no apparent trends associated with successively emplaced lava flows. The rheological properties of the lavas at the time of initial flow advance are therefore assumed to be comparable for each flow. Lava viscosity was estimated at 102 to 104 Pa s for the temperature range 1150 to 950 C. Yield strength was difficult to quantify but is assumed in this study to be relatively low (~ 25 Pa). Calculated flow velocity, effusion rate and emplacement duration are not well-constrained against documented eye-witness accounts. Mean flow velocity (0.03 to 0.04 m/s) was estimated from eye-witness reports, and used to determine flow emplacement durations between ~ 2 to 48 hours, comparable with documented duration times. Effusion rates could not be definitively quantified but flow deposit morphology and documented accounts indicate that intermittent episodes of high effusion rates over a short duration were associated with the emplacement of the 1954 lavas. 

Three major controls on the emplacement of the 1954 lava flows have been identified. Effusion rate and duration was the primary control on the development of single unit lava flows, flow channel drainage on steep slopes and in limiting run-out distances from the vent. Low initial viscosity and yield strength promoted high flow velocities on steep slopes and low surface cooling rates. Relatively short flow emplacement duration times precluded significant downflow viscosity and yield strength increases. Slope gradient and topographic obstacles were major controls on flow emplacement processes. Slope gradient was the dominant control on flow velocity, flow width and depth and surface autobrecciation, while morphology, flow path direction and surface folding were constrained by local slope gradient variations and/or topographic obstacles.

year: 2010

title: Correlations Between a Cyanobacteria Bloom's Decline and Environmental Dynamics.

authors: O'Rorke, Richard

subjects: cayanobacteria

abstract: Lake Kainui is an ombrogenous peat lake that is eutrophic and has frequent cyanobacterial blooms.  This research aimed to elucidate the factors that correlated with cyanobacterial bloom decline in Lake Kainui.  Abiotic and biotic variables in Lake Kainui were monitored weekly across the bloom decline phase.  Physicochemical parameters measured included nutrients, micronutrients, water temperature, dissolved oxygen (DO), pH and meteorological variables.  Planktonic and particle-associated bacterial community composition (BCC) was assessed through time using molecular fingerprinting (ARISA).  Total algal, cyanobacterial, planktonic bacteria, planktonic viruses and planktonic crustacean abundances were determined using microscopy.

The bloom decline coincided with multiple factors including; an increasing ratio of TN:TP, changes in the ratio of mixing depth (z¬mix) to euphotic depth (zeu) and pH.  The lake was stratified for several weeks before the decline and the resulting lake stability potentially created an adverse environment for cyanobacterial dominance.  Changes in planktonic biota were various.  Virus dynamics were positively correlated with phytoplankton dynamics.  If virus abundance was negatively correlated to phytoplankton diversity, it would potentially mean that viruses were controlling the phytoplankton assemblage, however virus abundance was positively correlated to phytoplankton diversity, which suggests that viruses had a positive impact on the bloom.  The positive effect was most likely due to to viruses upregulating the amount of dissolved organic matter through lysis.  Bacterial abundance showed no clear correlation with other variables, but bacterial community composition (BCC) shifted as the bloom declined.  Planktonic Cladocera spiked just after the bloom decline.  Bosmina was the dominant species of Cladocera, but was probably too small to ingest colonial Microcystis, which suggests that the Bosmina may be consuming degradation products produced by Microcystis.  These observations indicate that if planktonic biota played a role in bloom dynamics it was most likely due to shifts in the biota causing shifts in trophic cycling that alternately favour or disfavour blooming.

text: Correlations Between a Cyanobacteria Bloom's Decline and Environmental Dynamics. Lake Kainui is an ombrogenous peat lake that is eutrophic and has frequent cyanobacterial blooms.  This research aimed to elucidate the factors that correlated with cyanobacterial bloom decline in Lake Kainui.  Abiotic and biotic variables in Lake Kainui were monitored weekly across the bloom decline phase.  Physicochemical parameters measured included nutrients, micronutrients, water temperature, dissolved oxygen (DO), pH and meteorological variables.  Planktonic and particle-associated bacterial community composition (BCC) was assessed through time using molecular fingerprinting (ARISA).  Total algal, cyanobacterial, planktonic bacteria, planktonic viruses and planktonic crustacean abundances were determined using microscopy.

The bloom decline coincided with multiple factors including; an increasing ratio of TN:TP, changes in the ratio of mixing depth (z¬mix) to euphotic depth (zeu) and pH.  The lake was stratified for several weeks before the decline and the resulting lake stability potentially created an adverse environment for cyanobacterial dominance.  Changes in planktonic biota were various.  Virus dynamics were positively correlated with phytoplankton dynamics.  If virus abundance was negatively correlated to phytoplankton diversity, it would potentially mean that viruses were controlling the phytoplankton assemblage, however virus abundance was positively correlated to phytoplankton diversity, which suggests that viruses had a positive impact on the bloom.  The positive effect was most likely due to to viruses upregulating the amount of dissolved organic matter through lysis.  Bacterial abundance showed no clear correlation with other variables, but bacterial community composition (BCC) shifted as the bloom declined.  Planktonic Cladocera spiked just after the bloom decline.  Bosmina was the dominant species of Cladocera, but was probably too small to ingest colonial Microcystis, which suggests that the Bosmina may be consuming degradation products produced by Microcystis.  These observations indicate that if planktonic biota played a role in bloom dynamics it was most likely due to shifts in the biota causing shifts in trophic cycling that alternately favour or disfavour blooming.

year: 2009

title: Reo Rua Pukapuka Pikitia: Whānau drawing on their community cultural wealth to create strategies for developing Te Reo Rangatira

authors: Brouwer, Jacqui

abstract: The use of Te Reo Māori in Early Childhood Education in Aotearoa New Zealand is mandated in the ECE curriculum. Research shows that picturebooks are powerful tools in language learning, but there is a lack of research concerning the use of bilingual picturebooks by whānau to support Māori language learning in a New Zealand kindergarten. This research presents findings from a 4-week programme in which five whānau members were introduced to several types of dual language picturebooks (Reo Rua Pukapuka Pikitia, RRPP) in a Puna Pukapuka Pikitia (PPP). Whānau explored RRPP and suggested how they could bring Reo Rangatira from RRPP into their homes to support language learning. Their suggestions aligned with Ellis’s principles of effective language teaching (Ellis, 2010) including the development of formulaic phrases, following the ways in which tamariki naturally learn language, encouraging opportunities for tamariki to speak and listen, as well as having interactions linked to RRPP.

text: Reo Rua Pukapuka Pikitia: Whānau drawing on their community cultural wealth to create strategies for developing Te Reo Rangatira The use of Te Reo Māori in Early Childhood Education in Aotearoa New Zealand is mandated in the ECE curriculum. Research shows that picturebooks are powerful tools in language learning, but there is a lack of research concerning the use of bilingual picturebooks by whānau to support Māori language learning in a New Zealand kindergarten. This research presents findings from a 4-week programme in which five whānau members were introduced to several types of dual language picturebooks (Reo Rua Pukapuka Pikitia, RRPP) in a Puna Pukapuka Pikitia (PPP). Whānau explored RRPP and suggested how they could bring Reo Rangatira from RRPP into their homes to support language learning. Their suggestions aligned with Ellis’s principles of effective language teaching (Ellis, 2010) including the development of formulaic phrases, following the ways in which tamariki naturally learn language, encouraging opportunities for tamariki to speak and listen, as well as having interactions linked to RRPP.

year: 2023