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.

Microseismicity in the Eastern Alps: Preliminary Results From the Swath-D Network

2021 ◽  
Author(s):  
Rens Hofman ◽  
Joern Kummerow ◽  
Simone Cesca ◽  
Joachim Wassermann ◽  
Thomas Plenefisch ◽  
...  
Keyword(s):  
Large Data ◽  
Eastern Alps ◽  
Detection Methods ◽  
Mountain Range ◽  
Network Methods ◽  
Data Volume ◽  
Geophysical Processes ◽  
The Alps ◽  
Mountain Belts ◽  
Surrounding Areas

&lt;p&gt;The AlpArray seismological experiment is an international and interdisciplinary project to advance our understanding of geophysical processes in the greater Alpine region. The heart of the project consists of a large seismological array that covers the mountain range and its surrounding areas. To understand how the Alps and their neighbouring mountain belts evolved through time, we can only study its current structure and processes. The Eastern Alps are of prime interest since they currently demonstrate the highest crustal deformation rates. A key question is how these surface processes are linked to deeper structures. The Swath-D network is an array of temporary seismological stations complementary to the AlpArray network located in the Eastern Alps. This creates a unique opportunity to investigate high resolution seismicity on a local scale.&lt;/p&gt;&lt;p&gt;In this study, a combination of waveform-based detection methods was used to find small earthquakes in the large data volume of the Swath-D network. Methods were developed to locate the seismic events using semi-automatic picks, and estimate event magnitudes. We present an overview of the methods and workflow, as well as a preliminary overview of the seismicity in the Eastern Alps.&lt;/p&gt;

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.

scholarly journals Glacial limitation of tropical mountain height

2019 ◽  
Vol 7 (1) ◽  
pp. 147-169 ◽  
Author(s):  
Maxwell T. Cunningham ◽  
Colin P. Stark ◽  
Michael R. Kaplan ◽  
Joerg M. Schaefer
Keyword(s):  
Steady State ◽  
Mountain Range ◽  
Equilibrium Line Altitude ◽  
Glacial Erosion ◽  
Tropical Mountains ◽  
Base Level ◽  
Snow Line ◽  
Bedrock River Incision ◽  
High Tropical Mountains ◽  
The Tropics

Abstract. Absent glacial erosion, mountain range height is limited by the rate of bedrock river incision and is thought to asymptote to a steady-state elevation as erosion and rock uplift rates converge. For glaciated mountains, there is evidence that range height is limited by glacial erosion rates, which vary cyclically with glaciations. The strongest evidence for glacial limitation is at midlatitudes, where range-scale hypsometric maxima (modal elevations) lie within the bounds of Late Pleistocene snow line variation. In the tropics, where mountain glaciation is sparse, range elevation is generally considered to be fluvially limited and glacial limitation is discounted. Here we present topographic evidence to the contrary. By applying both old and new methods of hypsometric analysis to high mountains in the tropics, we show that (a) the majority are subject to glacial erosion linked to a perched base level set by the snow line or equilibrium line altitude (ELA) and (b) many truncate through glacial erosion towards the cold-phase ELA. Evaluation of the hypsometric analyses at two field sites where glacial limitation is seemingly marginal reveals how glaciofluvial processes act in tandem to accelerate erosion near the cold-phase ELA during warm phases and to reduce their preservation potential. We conclude that glacial erosion truncates high tropical mountains on a cyclic basis: zones of glacial erosion expand during cold periods and contract during warm periods as fluvially driven escarpments encroach and destroy evidence of glacial action. The inherent disequilibrium of this glaciofluvial limitation complicates the concept of time-averaged erosional steady state, making it meaningful only on long timescales far exceeding the interval between major glaciations.

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