Geological aspects of shallow landslides induced by the Heavy Rain Event of July 2018 within Late Cretaceous rhyolite, southern Hiroshima Prefecture, Japan

Author(s):  
Yasuto Hirata

<p>Rain-induced landslides often occur in clusters on hillslopes that have unique geological characteristics, such as lithology, weathering patterns, and hydrothermal alteration. However, the effects of geological factors on landslides involving rhyolites are not fully understood. A heavy rain event during July 2018 caused numerous debris avalanches and debris flows within areas underlain by the Late Cretaceous Takada Rhyolites, southern Hiroshima Prefecture, Japan. To understand the geological factors that influence landslides in areas underlain by rhyolites, we performed GIS analyses and field investigations of outcrops and landslide scars. The study area is rectangular, 9 km long, and 3 km wide, and the long sides, oriented NE–SW in Kure City. The Norosan Welded Tuff, which forms the rhyolite unit in the study area, has near-vertical joints spaced 0.1–5.0 m, and a large number of high-angle veinlets that record hydrothermal alteration. The average joint spacing is 1.8 m in the SW of the study area (0–3.5 km), decreases from 1.8 to 0.4 m in the center (3.5–5.0 km), and 0.4 m in the NE of the study area (5.0–9.0 km). Tors are developed on the ground surface on hillslopes in the SW of the study area, but the NE of the study area is underlain by clay-rich altered soil without corestones. The 45 h and 4 h cumulative rainfall distributions prior to the landslide event were similar in the SW and NE parts of the study area. Furthermore, the NE and SW parts of the study area have a comparable proportion of surface area with similar topographic parameters (slope, planar curvature, and catchment area) to those of landslide scars. In spite of these similarities, the landslide density is about ten times higher in the NE of the study area (10–55 /km<sup>2</sup>), than in the SW. This difference is attributed to differences in joint density, and the intense weathering and alteration on joints within the rhyolite.</p>

Weather ◽  
1998 ◽  
Vol 53 (8) ◽  
pp. 259-262
Author(s):  
C. C. Fu ◽  
C. C. Chan

2003 ◽  
Vol 129 (588) ◽  
pp. 495-522 ◽  
Author(s):  
Jean-François Georgis ◽  
Frank Roux ◽  
Michel Chong ◽  
Stephanie Pradier

2005 ◽  
Vol 20 (4) ◽  
pp. 397-414 ◽  
Author(s):  
Ryan E. Lyman ◽  
Thomas A. Schroeder ◽  
Gary M. Barnes

Abstract On 29 October 2000, the Hana region of Maui received 700 mm of rain in 7 h. Radar analyses revealed that the storm consisted of seven cells that were initiated along the southeast slope of Haleakala volcano. One of these cells survived for nearly 4 h and was responsible for 80% of the volumetric rainout from the storm. The interaction of low-level flow distorted by the island of Hawaii located farther east, the passage of a trough, and the topographic forcing caused by Haleakala volcano were major factors responsible for the evolution of the storm.


2019 ◽  
Vol 37 (4) ◽  
pp. 366-368
Author(s):  
Hidenori MORITA

2013 ◽  
Vol 10 (2) ◽  
pp. 2767-2790 ◽  
Author(s):  
S. Nagao ◽  
M. Kanamori ◽  
S. Ochiai ◽  
S. Tomihara ◽  
K. Fukushi ◽  
...  

Abstract. Effects of a heavy rain event on radiocesium export were studied at stations on the Natsui River and the Same River in Fukushima Prefecture, Japan after Typhoon Roke during 21–22 September 2011, six months after the Fukushima Daiichi Nuclear Power Plant accident. Radioactivity of 134Cs and 137Cs in river waters was 0.011–0.098 Bq L−1 at normal flow conditions during July–September in 2011, but it increased to 0.85 Bq L−1 in high flow conditions by heavy rains occurring with the typhoon. The particulate fractions of 134Cs and 137Cs were 21–56% in the normal flow condition, but were close to 100% after the typhoon. These results indicate that the pulse input of radiocesium associated with suspended particles from land to coastal ocean occurred by the heavy rain event. Export flux of 134Cs and 137Cs by the heavy rain accounts for 30–50% of annual radiocesium flux in 2011. Results show that rain events are one factor controlling the transport and dispersion of radiocesium in river watersheds and coastal marine environments.


2018 ◽  
Vol 18 (6) ◽  
pp. 2092-2099
Author(s):  
K. Doederer ◽  
Z. Ilieva ◽  
J. Keller

Abstract During disinfection, dissolved organic matter (DOM) is the major precursor to form disinfection by-products (DBPs), which may be of potential human health concern. Previous research focused on waters of continental climates and less on subtropical environments. However, water sources in subtropical climates are regularly impacted by major rain events during the summer months. This study evaluated the C- and N-DBP precursor removal capacity of two conventional ion exchange (IEX) resins and one magnetic ion exchange (MIEX) resin with a raw water at normal conditions and impacted by a heavy rain event. The rain event introduced 3 mg C/L total organic carbon (TOC) comprised mainly of low to medium molecular weight organics. All three resins were able to remove TOC and DBP precursors (>66%) but being less efficient in reducing turbidity (3–48%) and colour (9–24%). The resin with the smallest bead size was affected the most by the increased medium MW DOM loading resulting in DOM and C-DBP precursor removal performance losses of 10% and 22%. When applied as a pre-treatment for coagulation, MIEX was more efficient in DBP precursor control than coagulation in addressing the additional organic and DBP precursor loading after a heavy rain event.


SOLA ◽  
2019 ◽  
Vol 15A (0) ◽  
pp. 13-18 ◽  
Author(s):  
Akihiko Shimpo ◽  
Kazuto Takemura ◽  
Shunya Wakamatsu ◽  
Hiroki Togawa ◽  
Yasushi Mochizuki ◽  
...  

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