757 research outputs found
Holocene climate change and carbon cycling in a groundwater-fed,boreal forest lake: Dune Lake, Alaska
No full textGeographic and temporal variations in fire history in boreal ecosystems of Alaska
No full textCharcoal and pollen analyses were used to determine geographic and temporal patterns of fire importance in boreal forests of the Kenai Peninsula and interior Alaska. Sieved, large charcoal particles were measured in continuously sampled cores of Rock, Portage, and Arrow Lakes (Kenai Peninsula) and Dune and Deuce Lakes (interior Alaska) to estimate regional fire importance and fire occurrence. Charcoal accumulation rates have been low for the past 1000 years in both regions with slightly higher values in interior Alaska than on the Kenai Peninsula. An exception to this general pattern was the period of post-European settlement on the Kenai Peninsula, where charcoal accumulation rates increased by 10-fold. This increase most likely reflected increased fire occurrence due to human ignition. The Holocene charcoal and pollen records from Dune Lake indicate low fire occurrence during the early (9000 to 5500 calibrated year before present (yr BP)) birch-white spruce-alder (Betula-Picea glauca-Alnus) communities and high fire occurrence as black spruce (Picea mariana) became established after 5500 yr BP. Increased fires probably resulted from a change to fire-prone black spruce forests. For the past 5500 yr BP, two distinct fire regimes occurred. Frequent fires, with an average fire return interval of 98 years, characterized the period from 5500-2400 yr BP. Fewer fires, with an average fire interval of 198 years, characterized the period after 2400 yr BP. Fuel accumulation, stand structure, and vegetation species contributed to the natural variability in fire regimes during past changes in climate. <br/
The Archaeology Of Gua Tupak From 1,190 B.P. To 170 B.P. In Bau, Sarawak
No full textIn November and December 2007, an archaeological survey was conducted
by the author and a research team from the Centre for Global Archaeological
Research, Universiti Sains Malaysia, Penang with the cooperation of the Sarawak
Museum Department, Kuching in the limestone caves of the Bau area, southwest
Sarawak in order to search for a site for the author’s Master of Arts (MA) study. The
result of the survey determined Gua Tupak to be a highly potential site and
consequently, excavations were carried out at the site in February and March 2008.
The excavations at Gua Tupak yielded valuable archaeological data that could aid in
providing information on the prehistory of the site and the Bau area. The
archaeological data include various types of artefacts such as shell remains, animal
bones, ceramic sherds and stone artefacts. In addition, charcoal and shell samples
were collected for radiocarbon dating, soil samples were collected for palynological
analysis and soil profiles of the excavated trenches were recorded. Results of the
analyses of artefacts and interpretations of the archaeological data recovered from
Gua Tupak suggest that the site was used as a temporary habitation site or shelter
with two main phases of occupation; the Early Phase with a radiocarbon date of
around 1,190 ± 40 B.P., and the Late Phase with radiocarbon dates ranging from 270
± 50 B.P. to 170 ± 40 B.P
Agriculture facilitated permanent human occupation of the Tibetan Plateau after 3600 B.P.
No full textOur understanding of when and how humans adapted to living on the Tibetan Plateau at altitudes above 2000 to 3000 meters has been constrained by a paucity of archaeological data. Here we report data sets from the northeastern Tibetan Plateau indicating that the first villages were established only by 5200 calendar years before the present (cal yr B.P.). Using these data, we tested the hypothesis that a novel agropastoral economy facilitated year-round living at higher altitudes since 3600 cal yr B.P. This successful subsistence strategy facilitated the adaptation of farmers-herders to the challenges of global temperature decline during the late Holocene
Predictive mechanical model for fracture stimulation in an enhanced geothermal system (EGS) context
No full textAccepted Author ManuscriptReservoir EngineeringApplied Geolog
Location Changes of the Pit-Dwellings and Estimation of the Degree of the Tsunami Disaster Rate on Southern Sanriku Coast, Northeast Japan during the Jomon Period(ca 4700-2900 cal B.P.) : Cases of the Akahama-Ⅱ Site of Ootsuchi Bay and the Hamakawamesawada- I Site of Yamada Bay
No full textThe purpose of this study is to reconstruct the changing process of the altitudes over the sea of the pit-dwellings at Akahama-II site of Ootsuchi bay and Hamakawamesawada-I site of Yamada bay on the southern Sanriku coast, northeast Japan during the Jomon period(ca 4700-2900 cal B.P.) , and to estimate the degree of the tsunami disaster rate by using the inundation depth of the tsunami in the case of the 2011 Tohoku-oki earthquake.
The average altitudes of the pit-dwellings were 5.8m in around 4700 cal B.P., 3.7m in around 4600 cal B.P., and 2.5m in around 4200 cal B.P. in Akahama-II site, and were 6.9m in around 4700 cal B.P., 7.4m in around 4600 cal B.P., 6.5m in around 4500 cal B.P., and 1.6m in around 4000 cal B.P. in Hamakawame-sawada-I site.
There is a tendency to believe the inhabited period was older, the altitudes of the pit-dwellings were higher. There is also a possibility that there was not only the relative uplift of the coast in response to the sinking of the sea-level based on the Glacio-hydro Isostatic Adjustment theory, but also the actual elevation of the coast during 4700 cal B.P. and 4000 cal B.P..
On the other hand, the altitudes over the theoretical sea-level of the pit-dwellings around 4000 cal B.P.-4200 cal B.P. were too low for people to live there at both sites. It is necessary for people to live in the pit-dwellings over altitudes of at least 1 m because of the water level at high tide around the studied areas. It is estimated that the coast sank after around 4200 cal B.P..
The author puts forward that pit-dwellings during the Jomon period were hit by a tsunami that was the same level as the 2011 Tohoku-oki earthquake case, it is estimated that almost all of the pit-dwelings would have been affected by the tsunami at Akahama-II site and a few pit-dwellings would have been safe at Hamakawamesawada-I site.departmental bulletin pape
Evaluatie veldmetingen. Open taludbekledingen; bundeling huidige kennis
No full textIn het kader van het onderzoek aan open taludbekledingen zijn een drietal veldmeetmethoden ontwikkeld en toegepast. Daarnaast is het mogelijk het gedrag van een taludbekleding te voorspellen aan de hand van analytische relaties. Het gaat hierbij met name om de belasting op de toplaag ten gevolge van golfbelasting, en om overdrukken onder de toplaag die ontstaan indien de waterstand in de filterlaag een wisselende buitenwaterstand niet kan volgen. De drie meetmethoden zijn gebundeld in drie aparte verslagen, waarin ook de separate meetverslagen zijn te vinden. Dit verslag beoogt een overzicht te geven van de beschikbare methoden om doorlatendheden, lektijd en leklengte te bepalen. De ervaringen en resultaten worden met elkaar vergeleken. Hierdoor kan het toepassingsgebied van de diverse methodes worden aangegeven. Ten slotte volgen praktische aanwijzingen voor het bepalen van de eigenschappen van bestaande taludbekledingen.Steenzettingen - TAW/EN
Reststerkte van dijkbekledingen. Sterkte van klei onder golfbelasting
No full textDeel VI. Analyse van Deltagootmetingen In het kader van het onderzoek van de reststerkte van klei onder een dijkbekleding is een analyse verricht van de gemeten waterspanningen in en op het talud bij de reststerkteproeven, die zijn uitgevoerd in de Deltagoot in 1991/1992. De respons van de waterspanningsmeters is sterk afhankelijk van de locale condities in de klei. De optredende waterspanningsgradiënten zijn voldoende om klei uit het talud te lichten. Voor het juiste moment van het optreden van schade zijn cohesie- en interlock van de klei-aggregaten van belang. De toegebrachte erosieschade schaalt met de toegevoerde energie.Steenzettingen - TAW/EN
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