Review of ”How steady are steady-state mountain belts? – a re-examination of the Olympic Mountains (Washington State, USA)” by Michel et al.

2018 ◽  
Author(s):  
Anonymous
Keyword(s):  
Steady State ◽  
Washington State ◽  
Olympic Mountains ◽  
Mountain Belts

scholarly journals How steady are steady-state mountain belts? A reexamination of the Olympic Mountains (Washington state, USA)

2019 ◽  
Vol 7 (1) ◽  
pp. 275-299 ◽  
Author(s):  
Lorenz Michel ◽  
Christoph Glotzbach ◽  
Sarah Falkowski ◽  
Byron A. Adams ◽  
Todd A. Ehlers
Keyword(s):  
Steady State ◽  
Washington State ◽  
Cascadia Subduction Zone ◽  
Mountain Range ◽  
Accretionary Wedge ◽  
Pleistocene Glaciation ◽  
Kinematic Modeling ◽  
Olympic Mountains ◽  
Mountain Belts ◽  
Exhumation Rates

Abstract. The Olympic Mountains of Washington state (USA) represent the aerially exposed accretionary wedge of the Cascadia Subduction Zone and are thought to be in flux steady state, whereby the mass outflux (denudation) and influx (tectonic accretion) into the mountain range are balanced. We use a multi-method approach to investigate how temporal variations in the influx and outflux could affect previous interpretations of flux steady state. This includes the analysis of published and new thermochronometric ages for (U–Th) ∕ He dating of apatite and zircon (AHe and ZHe, respectively), fission-track dating of apatite and zircon (AFT and ZFT, respectively), 1-D thermo-kinematic modeling of thermochronometric data, and independent estimates of outflux and influx. In total, we present 61 new AHe, ZHe, AFT, and ZFT thermochronometric ages from 21 new samples. AHe ages are generally young (< 4 Ma), and, in some samples, AFT ages (5–8 Ma) overlap ZHe ages (7–9 Ma) within uncertainties. Thermo-kinematic modeling shows that exhumation rates are temporally variable, with rates decreasing from > 2 to < 0.3 km Myr−1 around 5–7 Ma. With the onset of Plio–Pleistocene glaciation, exhumation rates increased to values > 1 km Myr−1. This demonstrates that the material outflux varies through time, requiring a commensurate variation in influx to maintain flux steady state. Evaluation of the offshore and onshore sediment record shows that the material influx is also variable through time and that the amount of accreted sediment in the wedge is spatially variable. This qualitatively suggests that significant perturbations of steady state occur on shorter timescales (105–106 years), like those created by Plio–Pleistocene glaciation. Our quantitative assessment of influx and outflux indicates that the Olympic Mountains could be in flux steady state on long timescales (107 years).

scholarly journals How steady are steady-state mountain belts? – a re-examination of the Olympic Mountains (Washington State, USA)

2018 ◽  
Author(s):  
Lorenz Michel ◽  
Christoph Glotzbach ◽  
Sarah Falkowski ◽  
Byron A. Adams ◽  
Todd A. Ehlers
Keyword(s):  
Steady State ◽  
Temporal Variations ◽  
Washington State ◽  
Cascadia Subduction Zone ◽  
Mountain Range ◽  
Accretionary Wedge ◽  
Olympic Mountains ◽  
Kinematic Modelling ◽  
Multi Method Approach ◽  
Mountain Belts

Abstract. The Olympic Mountains of Washington State (USA) represent the aerially exposed accretionary wedge of the Cascadia subduction zone and are thought to be in flux steady-state, whereby the mass outflux (denudation) and influx (tectonic accretion) into the mountain range are balanced. We use a multi-method approach to investigate how temporal variations in the influx and outflux could affect previous interpretations of flux steady-state. This includes published and new thermochronometric ages for (U-Th)/He dating of apatite and zircon (AHe and ZHe, respectively) and fission track dating of apatite and zircon (AFT and ZFT, respectively), 1D thermo-kinematic modelling of thermochronometric data and independent estimates of outflux and influx. We present 61 new thermochronometric ages. AHe ages are generally young ( 2 km/Myr to  1 km/Myr. This demonstrates that the material outflux is varying through time, requiring a commensurate variation in influx to maintain flux steady-state. Evaluation of the offshore and onshore sediment record shows, that the material influx is also variable through time and that the amount of sediment residing in the wedge is spatially variable. Our quantitative assessment of influx and outflux indicates that the Olympic Mountains could be in flux steady-state on long timescales (107 yr), but significant perturbations of steady-state occur on shorter timescales (105–106 yr), e.g., during the Plio-Pleistocene glaciation.

scholarly journals The Sensitivity of Orographic Precipitation to Flow Direction: An Idealized Modeling Approach

2017 ◽  
Vol 18 (6) ◽  
pp. 1673-1688 ◽  
Author(s):  
Lee Picard ◽  
Clifford Mass
Keyword(s):  
Pacific Northwest ◽  
Wind Direction ◽  
Flow Direction ◽  
Three Dimensional ◽  
Washington State ◽  
Directional Sensitivity ◽  
Orographic Precipitation ◽  
Major Question ◽  
Olympic Mountains ◽  
Physics Model

Abstract A major question regarding orographic precipitation is its sensitivity to flow direction, with some research suggesting substantial sensitivity. To examine this issue, this paper describes a full physics model with realistic three-dimensional terrain that is forced by a single input sounding. This system is used to investigate the sensitivity of orographic precipitation to wind direction over the Pacific Northwest for conditions approximating an atmospheric river. The model results show considerable modulation of regional precipitation as flow direction changes, with results for four Washington State river drainages agreeing well with previous observational studies. It is shown that precipitation amounts over such drainages can vary substantially with very small changes in the direction of the incoming flow. To explore the origin of directional sensitivity of precipitation over the Olympic Mountains of western Washington State, additional experiments were carried out using modified terrain fields with smoothed or idealized Olympic Mountains, or with nearby orography removed. These simulations suggest that the sensitivity of Olympic Mountain precipitation to wind direction is more strongly modulated by the presence of surrounding orography than by the specific geometry of the Olympic Mountains.

Topographic evolution of mountain belts controlled by rheology and surface process efficiency

2020 ◽  
Author(s):  
Sebastian G. Wolf ◽  
Ritske S. Huismans ◽  
Jean Braun ◽  
Xiaoping Yuan
Keyword(s):  
Steady State ◽  
Process Efficiency ◽  
Surface Process ◽  
Tight Coupling ◽  
Active Growth ◽  
Term Survival ◽  
Erosion Rates ◽  
Mountain Belt ◽  
Tectonically Active ◽  
Mountain Belts

&lt;p&gt;It has been a long-standing problem how mountain belts gain and loose topography during their tectonically active growth and inactive decay phase. It is widely recognized that mountain belt topography is generated by crustal shortening, and lowered by river bedrock erosion, linking climate to tectonics. However, it remains enigmatic how to reconcile high erosion rates in active orogens as observed in Taiwan or New Zealand, with long term survival of topography for 100s of Myrs as observed for example in the Uralides and Appalachians. Here we use for the first time a tight coupling between a landscape evolution model (FastScape) with an upper mantle scale tectonic (thermo-mechanical) model to investigate the different stages of mountain belt growth and decay. Using two end-member models, we demonstrate that growing orogens with high erosive power remain small (&lt;200 km), reach steady state between tectonic in- and erosional material eff-flux, and are characterized by transverse valleys. Contrarily, mountain belts with medium to low erosive power will not reach growth steady state, grow wide, and are characterized by longitudinal rivers deflected by active thrusting. However, during growth both types of orogens reach the same height, controlled by rheology and independent of surface process efficiency. Erosional efficiency controls orogenic decay, which is counteracted by regional isostatic rebound. Rheological control of mountain height implies that there is a natural upper limit for the steepness index of rivers on Earth. To compare model results to various natural examples, we quantify the degree of longitudinal flow of modeled rivers with river &amp;#8220;longitudinality&amp;#8221; in several active or recently active orogens on Earth. Application of the river &amp;#8220;longitudinality index&amp;#8221; gives information whether (parts of) an orogen is or was at steady state during orogenic growth.&lt;/p&gt;

scholarly journals Effect of Area Distribution with Altitude on Glacier Mass Balance – A Comparison of North and South Klawatti Glaciers, Washington State, U.S.A.

1990 ◽  
Vol 14 ◽  
pp. 278-282 ◽  
Author(s):  
Wendell V. Tangborn ◽  
Andrew G. Fountain ◽  
William G. Sikonia
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Quadratic Equation ◽  
Washington State ◽  
Mass Change ◽  
Glacier Mass Balance ◽  
The North ◽  
Calculated Mass ◽  
Longitudinal Profiles ◽  
North And South

The North and South Klawatti glaciers are adjacent glaciers in the North Cascade Mountains of Washington state. During 1947–61 North Klawatti Glacier lost volume, equivalent to a mean decrease in thickness of 8.3 m over the glacier area, whereas South Klawatti Glacier gained volume, equivalent to an increase in thickness of 5.8 m. Although the glaciers are in the same climate, they have different distributions of area with altitude, resulting in different responses to climatic variations.A quadratic equation is assumed to approximate the relation of mass balance to altitude for both Klawatti glaciers. The coefficients of the equation are derived by comparing the calculated mass change to the mass change for each glacier estimated from topographic maps. The resultant relation of mass balance to altitude is the mean for the time period between maps (1947–61).Steady-state longitudinal profiles of both glaciers were obtained by shifting the existing mass-balance versus altitude curve by a magnitude equal to the measured mean annual mass balance. To produce steady-state conditions, the equilibrium-line altitudes of both glaciers would need to move less than 90 m (85 m higher for South Klawatti Glacier and 88 m lower for North Klawatti Glacier).

scholarly journals Extracting information on the spatial variability in erosion rate stored in detrital cooling age distributions in river sands

2017 ◽  
Author(s):  
Jean Braun ◽  
Lorenzo Gemignani ◽  
Peter van der Beek
Keyword(s):  
Steady State ◽  
Spatial Variability ◽  
Erosion Rate ◽  
Regional Scale ◽  
River System ◽  
Eastern Himalaya ◽  
Relative Distribution ◽  
Simple Method ◽  
Erosion Rates ◽  
Mountain Belts

Abstract. The purpose of detrital thermochronology is to provide constraints on regional scale exhumation rate and its spatial variability in actively eroding mountain ranges. Procedures that use cooling age distributions coupled with hypsometry and thermal models have been developed in order to extract quantitative estimates of erosion rate and its spatial distribution, assuming steady state between tectonic uplift and erosion. This hypothesis precludes the use of these procedures to assess the likely transient response of mountain belts to changes in tectonic or climatic forcing. In this paper, we describe a simple method that, using the observed detrital mineral age distributions collected in a system of river catchments, allows to extract information about the relative distribution of erosion rates in an eroding hinterland without relying on a steady-state assumption or the value of thermal parameters. The model is based on a relatively low number of parameters describing lithological variability among the various catchments and their sizes, and only uses the raw binned ages. In order to illustrate the method, we invert age distributions collected in the Eastern Himalaya, one of the most tectonically active places on Earth. From the inversion of the cooling age distributions we predict present day erosion rates of the catchments along the Siang-Tsangpo-Brahmaputra river system, as well as smaller tributaries. We show that detrital age distributions contain dual information about present-day erosion rate, i.e. from the predicted distribution of surface ages within each catchment and from the relative contribution of any given catchment to the river distribution. The inversion additionally allows comparing modern erosion rates to long-term exhumation rates. We provide a simple implementation of the method in R.code within a Jupyter Notebook that includes the data used in this paper for illustration purposes.

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