scholarly journals Extreme event-driven sediment aggradation and erosional buffering along a tectonic gradient in southern Taiwan

Geology ◽  
2021 ◽  
Author(s):  
Clarke DeLisle ◽  
Brian J. Yanites ◽  
Chia-Yu Chen ◽  
Bruce H. Shyu ◽  
Tammy M. Rittenour
Keyword(s):  
Extreme Event ◽  
Landscape Evolution ◽  
Extreme Rainfall ◽  
Tectonic Activity ◽  
Stream Power ◽  
Sediment Delivery ◽  
Landscape Response ◽  
Tectonically Active ◽  
Southern Taiwan ◽  
Sediment Cover

In most landscape evolution models, extreme rainfall enhances river incision. In steep landscapes, however, these events trigger landslides that can buffer incision via increased sediment delivery and aggradation. We quantify landslide sediment aggradation and erosional buffering with a natural experiment in southern Taiwan where a northward gradient in tectonic activity drives increasing landscape steepness. We find that landscape response to extreme rainfall during the 2009 typhoon Morakot varied along this gradient, where steep areas experienced widespread channel sediment aggradation of >10 m and less steep areas did not noticeably aggrade. We model sediment export to estimate a sediment removal timeline and find that steep, tectonically active areas with the most aggradation may take centuries to resume bedrock incision. Expected sediment cover duration reflects tectonic uplift. We find that despite high stream power, sediment cover may keep steep channels from eroding bedrock for up to half of a given time period. This work highlights the importance of dynamic sediment cover in landscape evolution and suggests a mechanism by which erosional efficiency in tectonically active landscapes may decrease as landscape steepness increases.

Impact of fires, earthquakes, and climate on catchment response since 600 CE, Pallett Creek, San Gabriel Mountains, Southern California USA

2021 ◽  
Author(s):  
Katherine Scharer ◽  
Jenifer Leidelmeijer ◽  
Matthew Kirby ◽  
Nicole Bonuso ◽  
Devin McPhillips
Keyword(s):  
Southern California ◽  
Active Regions ◽  
Ice Age ◽  
Sedimentation Rates ◽  
Sediment Delivery ◽  
San Gabriel Mountains ◽  
High Sedimentation ◽  
Landscape Response ◽  
Tectonically Active ◽  
The Impact

<div> <p>In tectonically active regions, sedimentary records are overprinted by landscape response to climate, fire, and local earthquakes.  We explore this issue using a new paleoclimate record developed at the Pallett Creek paleoseismic site in southern California USA, a recently incised distal fan located along the San Andreas Fault at the base of a 35 km<sup>2</sup> catchment in the San Gabriel Mountains.  To date, we have analyzed 6 m of section, spanning the last 1300 yr, for grain size, total organic material (TOM), carbon/nitrogen (C/N) ratios, magnetic susceptibility, and charcoal count. Existing C-14 dates (Scharer et al., 2011) inform rates of sediment deposition and charcoal accumulation (CHAR). Additional dating and macrofossil analysis is ongoing.  Sedimentological variability within the section is dominated by two general units. Unit 1 is characterized by high % clay, % silt, and % TOM, while Unit 2 is distinctly coarser with higher % sand and lower % TOM.  Pulses of high CHAR occur from 1150-1260 yr BP and during the Little Ice Age (100-500 yr BP) and are associated with high sedimentation rates (0.3-2 cm/yr), while only a few relatively weak fire episodes are recorded in the Medieval Climate Anomaly (700-1000 yr BP), despite similarly high sedimentation rates (0.6 cm/yr).  Ten earthquakes documented at the site (Sieh et al., 1989) occurred about every 135 years and impart no obvious short-term impact on sedimentation rates, perhaps reflecting the distance between the site and steeper portions of the drainage network (>4 km) likely to produce mass wasting.  Overall, the landscape response of this large, integrated catchment appears to reflect a stronger influence of fire and climate than earthquakes. Future work will focus on the impact of the fire episodes on sediment delivery and resultant paleoearthquake ages.</p> </div>

scholarly journals Statistical modelling of co-seismic knickpoint formation and river response to fault slip

2019 ◽  
Vol 7 (3) ◽  
pp. 681-706
Author(s):  
Philippe Steer ◽  
Thomas Croissant ◽  
Edwin Baynes ◽  
Dimitri Lague
Keyword(s):  
Landscape Evolution ◽  
Fault Slip ◽  
Tectonic Activity ◽  
Aseismic Slip ◽  
Seismic Slip ◽  
Topographic Data ◽  
Negative Exponential Distribution ◽  
Sediment Cover ◽  
River Profiles

Abstract. Most landscape evolution models adopt the paradigm of constant and uniform uplift. It results that the role of fault activity and earthquakes on landscape building is understood under simplistic boundary conditions. Here, we develop a numerical model to investigate river profile development subjected to fault displacement by earthquakes and erosion. The model generates earthquakes, including mainshocks and aftershocks, that respect the classical scaling laws observed for earthquakes. The distribution of seismic and aseismic slip can be partitioned following a spatial distribution of mainshocks along the fault plane. Slope patches, such as knickpoints, induced by fault slip are then migrated at a constant rate upstream a river crossing the fault. A major result is that this new model predicts a uniform distribution of earthquake magnitude rupturing a river that crosses a fault trace and in turn a negative exponential distribution of knickpoint height for a fully coupled fault, i.e. with only co-seismic slip. Increasing aseismic slip at shallow depths, and decreasing shallow seismicity, censors the magnitude range of earthquakes cutting the river towards large magnitudes and leads to less frequent but higher-amplitude knickpoints, on average. Inter-knickpoint distance or time between successive knickpoints follows an exponential decay law. Using classical rates for fault slip (15 mm year−1) and knickpoint retreat (0.1 m year−1) leads to high spatial densities of knickpoints. We find that knickpoint detectability, relatively to the resolution of topographic data, decreases with river slope that is equal to the ratio between fault slip rate and knickpoint retreat rate. Vertical detectability is only defined by the precision of the topographic data that sets the lower magnitude leading to a discernible offset. Considering a retreat rate with a dependency on knickpoint height leads to the merging of small knickpoints into larger ones and larger than the maximum offset produced by individual earthquakes. Moreover, considering simple scenarios of fault burial by intermittent sediment cover, driven by climatic changes or linked to earthquake occurrence, leads to knickpoint distributions and river profiles markedly different from the case with no sediment cover. This highlights the potential role of sediments in modulating and potentially altering the expression of tectonic activity in river profiles and surface topography. The correlation between the topographic profiles of successive parallel rivers cutting the fault remains positive for distance along the fault of less than half the maximum earthquake rupture length. This suggests that river topography can be used for paleo-seismological analysis and to assess fault slip partitioning between aseismic and seismic slip. Lastly, the developed model can be coupled to more sophisticated landscape evolution models to investigate the role of earthquakes on landscape dynamics.

scholarly journals Assessment of Rainfall-Induced Landslide Distribution Based on Land Disturbance in Southern Taiwan

2021 ◽  
Vol 10 (4) ◽  
pp. 209
Author(s):  
Chih-Ming Tseng ◽  
Yie-Ruey Chen ◽  
Chwen-Ming Chang ◽  
Yung-Sheng Chue ◽  
Shun-Chieh Hsieh
Keyword(s):  
Satellite Image ◽  
Extreme Rainfall ◽  
Land Area ◽  
Rainfall Events ◽  
Land Disturbance ◽  
Bare Land ◽  
Southern Taiwan ◽  
The Impact ◽  
Landslide Distribution ◽  
The Relationship

This study explores the impact of rainfall on the followed-up landslides after a severe typhoon and the relationship between various rainfall events and the occurrence, scale, and regional characteristics of the landslides, including second landslides. Moreover, the influence of land disturbance was evaluated. The genetic adaptive neural network was used in combination with the texture analysis of the geographic information system for satellite image classification and interpretation to analyze land-use change and retrieve disaster records and surface information after five rainfall events from Typhoon Morakot (2009) to Typhoon Nanmadol (2011). The results revealed that except for extreme Morakot rains, the greater the degree of slope disturbance after rain, the larger the exposed slope. Extreme rainfall similar to Morakot strikes may have a greater impact on the bare land area than on slope disturbance. Moreover, the relationship between the bare land area and the index of land disturbance condition (ILDC) is positive, and the ratio of the bare land area to the quantity of bare land after each rainfall increases with the ILDC. With higher effective accumulative rainfall on the slope in the study area or greater slope disturbance, the landslide area at the second landslide point tended to increase.

scholarly journals Landscape evolution models using the stream power incision model show unrealistic behavior when <i>m</i> ∕ <i>n</i> equals 0.5

2017 ◽  
Vol 5 (4) ◽  
pp. 807-820 ◽  
Author(s):  
Jeffrey S. Kwang ◽  
Gary Parker
Keyword(s):  
Steady State ◽  
Landscape Evolution ◽  
Drainage Area ◽  
Uplift Rate ◽  
Stream Power ◽  
River Incision ◽  
Vertical Incision ◽  
Small Scales ◽  
Insight Into

Abstract. Landscape evolution models often utilize the stream power incision model to simulate river incision: E = KAmSn, where E is the vertical incision rate, K is the erodibility constant, A is the upstream drainage area, S is the channel gradient, and m and n are exponents. This simple but useful law has been employed with an imposed rock uplift rate to gain insight into steady-state landscapes. The most common choice of exponents satisfies m ∕ n = 0.5. Yet all models have limitations. Here, we show that when hillslope diffusion (which operates only on small scales) is neglected, the choice m ∕ n = 0.5 yields a curiously unrealistic result: the predicted landscape is invariant to horizontal stretching. That is, the steady-state landscape for a 10 km2 horizontal domain can be stretched so that it is identical to the corresponding landscape for a 1000 km2 domain.

scholarly journals Landslide susceptibility assessment in the Peloritani Mts. (Sicily, Italy) and clues for tectonic control of relief processes

2013 ◽  
Vol 13 (4) ◽  
pp. 949-963 ◽  
Author(s):  
G. De Guidi ◽  
S. Scudero
Keyword(s):  
Spatial Data ◽  
Landslide Susceptibility ◽  
Landscape Evolution ◽  
Statistical Technique ◽  
Slope Instability ◽  
Tectonic Activity ◽  
Medium Term ◽  
Tectonic History ◽  
Susceptibility Model ◽  
Morphological Processes

Abstract. Many destructive shallow landslides hit villages in the Peloritani Mountains area (Sicily, Italy) on 1 October 2009 after heavy rainfall. The collection of several types of spatial data, together with a landslide inventory, allows the assessment of the landslide susceptibility by applying a statistical technique. The susceptibility model was validated by performing an analysis in a test area using independent landslide information, the results being able to correctly predict more than 70% of the landslides. Furthermore, the susceptibility analysis allowed the identification of which combinations of classes, within the different factors, have greater relevance in slope instability, and afterwards associating the most unstable combinations (with a short–medium term incidence) with the endogenic processes acting in the area (huge regional uplift, fault activity). Geological and tectonic history are believed to be key to interpreting morphological processes and landscape evolution. Recent tectonic activity was found to be a very important controlling factor in landscape evolution. A geomorphological model of cyclical relief evolution is proposed in which endogenic processes are directly linked to superficial processes. The results are relevant both to risk reduction and the understanding of active geological dynamics.

scholarly journals Large Evaporite Provinces: Geothermal rather than Solar Origin?

2020 ◽  
Author(s):  
Zhanjie Qin ◽  
Chunan Tang ◽  
Xiying Zhang ◽  
Tiantian Chen ◽  
Xiangjun Liu ◽  
...  
Keyword(s):  
Large Scale ◽  
Climatic Factors ◽  
Temporal Distribution ◽  
Tectonic Activity ◽  
Driving Mechanism ◽  
Solar Origin ◽  
Tectonically Active ◽  
Spatio Temporal ◽  
Thermal Influence ◽  
The Masses

Abstract Large evaporite provinces (LEPs) represent prodigious volumes of evaporites widely developed from the Sinian to Neogene. The reasons why they often quickly develop on a large scale with large areas and thicknesses remain enigmatic. Possible causes range from warming from above to heating from below. The fact that the salt deposits in most salt-bearing basins occur mainly in the Sinian-Cambrian, Permian-Triassic, Jurassic-Cretaceous, and Miocene intervals favours a dominantly tectonic origin rather than a solar driving mechanism. Here, we analysed the spatio-temporal distribution of evaporites based on 138 evaporitic basins and found that throughout the Phanerozoiceon, LEPs occurred across the Earth’s surface in most salt-bearing basins, especially in areas with an evolutionary history of strong tectonic activity. The masses of evaporites, rates of evaporite formation, tectonic movements, and large igneous provinces (LIPs) synergistically developed in the Sinian-Cambrian, Permian, Jurassic-Cretaceous, and Miocene intervals, which are considered to be four of the warmest times since the Sinian. We realize that salt accumulation can proceed without solar energy and can generally be linked to geothermal changes in tectonically active zones. When climatic factors are involved, they may be manifestations of the thermal influence of the crust on the surface.

scholarly journals Evaluation of hillslope failure and community adjustment after extreme weather event, Waimarama 26-27 April, 2011

2021 ◽  
Author(s):  
◽  
Albert Edward Frampton
Keyword(s):  
Water Content ◽  
Small Businesses ◽  
Extreme Event ◽  
Extreme Rainfall ◽  
Field Measurements ◽  
Economic Loss ◽  
Laboratory Analysis ◽  
Annual Rainfall ◽  
Financial Loss ◽  
North West

<p>In 2011, Waimarama received 80% of its annual rainfall in 48 hours. This extreme event with a return period of >100 years caused saturated hillslopes to collapse forming 100s of shallow landslides in the Puhokio Valley. This study collected soil samples from 54 exposed slip scarp horizons for laboratory analysis of soil mechanical properties. Field measurements of slip and slope angles, length, width and depth to determine that 23,212m³ of sediment was volume lost, from the 54 landslides. The field and lab measurements were used to generate a coherent understanding of landsliding at Waimarama. Laboratory analysis for liquid limits water content showed a high of 88.5% to a low of 18.8% and plastic limit water content had a high of 51% in the A horizon (organics) and low of 16.1%. Specific gravity also indicated a high reading 1.74 g/cm³ with a low of 1.16 g/cm³. The A horizon was able to tolerate high levels of water content in most tests, while the B horizon was capable of coping with some increase in water content. The C horizon was only able to handle low volumes of water, and was the main initiator of regolith collapse. The laboratory results indicated high saturation levels within the horizons of weak lithology of marine regolith that over caps impervious marine bedrock. The main cause for hillslope collapse and exposure of multiple translational and debris flow landslides was extreme saturation. However, towards the height of the rainfall event a 4.5 magnitude earthquake was recorded with unknown collateral consequences. Most slip locations were found in the aspects of east, south-east, west, and north-west, and on slope angles 15 -25°. The study confirmed previous surveys that regolith depth 80-100cm on impervious sandstone, siltstone/mudstone, when saturated over lengthy wet spells or from extreme precipitation, will collapse. In addition to the physical geographic study a survey was included to record individual and family accounts of the weather phenomenon. A questionnaire was prepared with specific questions that required yes or no answers. These questions dealt with loss of buildings, loss of land, animals, financial loss and recovery, economic loss, insurance and mitigation plans. The most affected were farmers and the next affected were householders while the holiday park was the worst affected of small businesses. Insurance was a significant help in most recoveries. Land rehabilitation was mitigated with new plantings and some aerial sowing, otherwise many slips were left to revegetate naturally. Economic and financial loss was severe for most farmers, due to pasture loss and animal relocation. Extreme rainfall causes slips that affect humans, but they can be mitigated. The Waimarama event is one of many events that can happen countrywide, the results can be a disastrous loss of personal, economic and financial assets, loss of infrastructure, including roading, bridges and communication. These are factors that many people and communities only realise when it happens to them. Mitigation against such events might include adequate insurance and knowledge of what to do, and where to go should an event happen unexpectedly and without warning.</p>

Delineating active faults across the Narmada-Son Lineament (NSL), India using the technique of Fracture Induced Electromagnetic Radiation (FEMR)

2021 ◽  
Author(s):  
Shreeja Das ◽  
Jyotirmoy Mallik
Keyword(s):  
Electromagnetic Radiation ◽  
Process Zone ◽  
Active Faults ◽  
Central India ◽  
Earthquake Forecasting ◽  
Tectonic Activity ◽  
Eurasian Plate ◽  
Near Surface ◽  
Crustal Stresses ◽  
Tectonically Active

&lt;p&gt;The Fracture Induced Electromagnetic Radiation (FEMR) technique has gradually progressed in the past decade as a useful geophysical tool to determine the direction and magnitude of recent crustal stresses, visualize the modification and realignment of stresses inside tunnels thus proving to be an important precursor for geohazards, earthquake forecasting, as well as delineate landslide-prone slip planes in unstable regions. Its working principle is based on the generation of geogenic electromagnetic radiation emanating from the brittle rock bodies that are fractured being subjected to an incremental increase of the differential stress in the near-surface of the Earth&amp;#8217;s crust. The &amp;#8220;Process zone&amp;#8221; at the fractured crack tip contains numerous microcracks which subsequently creates dipoles due to the polarization of charges on such microcrack tips which rapidly oscillates emitting FEMR waves of frequencies between KHz to MHz range. The coalescence of the microcracks eventually leads to a macro failure dampening the amplitude of the FEMR pulses. The attenuation of FEMR pulses is comparatively lesser than seismic waves making it a more efficient precursor to potential tectonic activities indicating an upcoming earthquake a few hours/days before the actual event. In the current study, we have attempted to exploit this technique to identify the locations of the potential active faults across the tectonically active Narmada-Son Lineament (NSL), Central India. Although the first tectonic stage involved rifting and formation of the NSL during the Precambrian time, the rifting continued at least till the time of Gondwana deposition. Later, tectonic inversion took place as a result of the collision between the Indian and the Eurasian plate resulting in reverse reactivation of the faults. Episodic reverse movement along NSL caused recurrent earthquakes and linear disposition of the sediments that were deposited at the foothills of the Satpura Horst. Although the origin of East-West trending NSL dates back to the Precambrian time, it is very much tectonically active as manifested by recent earthquakes. The study has been conducted by taking linear FEMR readings across 3 traverses along the NSL which on analysis provides an idea about the potential active faults, their locations, and frequency of occurrence. The accumulation of strain in the brittle rocks that can eventually lead to a macro failure is demarcated as an anomalous increase in the amplitude of the FEMR pulses indicative of an upcoming tectonic episode in the region. To further corroborate the analysis, we have attempted to determine the neo-tectonic activity in the region by calculating the morphometric parameters across the Khandwa-Itarsi-Jabalpur region, Central India. Finally, we attempt to comment on the tectonic evolution of Central India in the recent past. We also encourage researchers to adapt the novel technique of FEMR which is swift, affordable, and feasible compared to conventional techniques deployed to survey the active tectonics of a region.&lt;/p&gt;

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