Monday, 16 November 2015

The survey of Lake Kawaguchi is already done !



We finished the coring in Lake Kawaguchi, it was a real success!  Lake Kawaguchi is a shallow lake with a maximum depth of 12 m. It is characterized by three sub-basins – Western, central and East basins. We investigated two sites, one in the western basin and one in the central basin.


Sunday, 8 November 2015

The Fuji Five Lake survey has started !



On Monday, the platform arrived from Hamana-ko to Kawaguchi-ko. At the end of the day, we were ready to core. The aim of the survey is to get long cores from the Fuji Five Lakes in order to retrieve the seismic history of the Nankai Through. During this month, we will investigate Lake Kawaguchi, Lake Motosu and Lake Sai. We will spend one week in Lake Kawaguchi and Lake Sai. Our best target is the Lake Motosu where we will be for two weeks. This year, we decide to not investigate Lake Yamanaka for several reasons. Lake Yamanaka is very close to Fuji volcano and highly exposed to eruptions. The study of the 1998 old borehole revealed a lot of scoria layers and we were not sure that our equipment could go through them. Because our coring system was struck in Hoei scoria (1707A.D.), the age of short cores taken last year is relatively well constrained. In 300 years, Lake Yamanaka has not recorded any turbidites. This is why, this year, we will focus on the other three lakes. In our long cores, we expect to find turbidites triggered by earthquake that allow us to compare the earthquake fingerprint of each lake… But first, we need to hammer!

The platform on Lake Kawaguchi

Thursday, 5 November 2015

Every end is a new beginning

Our working days on coastal Lake Hamana are now definitively over. The platform has been relocated to the Fuji area, where coring operations on Lake Kawaguchi were started.  

Unfortunately, we did not succeed in retrieving all missing core sections on site 3 and site 4 of Lake Hamana, since very strong winds threw a spanner in the works and we were not able to sail out during the last two days. Nevertheless, we now possess sediment samples up to a depth of 9 m below the lake floor, from four different locations along a N-S transect throughout the central basin. Such transect allows us to map the extent and lateral variations of tsunami deposits, which will be traced by executing a series of sedimentological, geophysical and geochemical analyses.


But first… our cores have to be shipped back to Belgium. This will be done at the end of November, after the Fuji survey is finished as well.

Sneak peaks of Mount Fuji from Lake Hamana

Sunday, 25 October 2015

Entering the last week

Having the checkered flag of our Lake Hamana piston coring mission in sight, we can already look back at many days of hard work and dedication. However, we still need to complete a few things.

We have been sampling sediment from four consecutive sites along a N-S transect within the lake’s central basin, north of the tidal delta. Two of these sites are entirely finished (site 1 and 2), whereas we still have to take six more 2 m piston core sections from the northern two sites (site 3 and 4).   

Location map of Lake Hamana (left) and bathymetry of the lake basin with indication of our coring sites, yellow ones are finished, red ones still need to be completed (right)

Sunday, 18 October 2015

If I had a hammer…

I’d hammer in the morning, I’d hammer in the evening…

Two weeks have passed since we started taking cores from our platform on Lake Hamana and loads of mud and sand has been lifted out of the lake floor. Our Belgian coring team is starting to work like a well-oiled machine. Hence, about time to introduce you to our floating home and how we manage to sample more than 8 m of bottom stratigraphy.

Our platform is held in position by four anchors and consists of four rubber floaters, a 3x4 m standing surface with a central opening and a tripod to which three winches are fastened. Each of these winches holds part of the coring equipment, which is guided through pulleys at the crest of the tripod. One winching cable is attached to the hammer weight, one to the piston and one to the entire system (coring barrel, hammer weight and piston).


Leaving the marina

Sunday, 11 October 2015

A new field season for QRN

Last year (Oct-Nov), the QRN team came together in Japan for conducting exploratory surveys on the Fuji Lakes and the coastal Hamana lake area. This exploration comprised the acoustic imaging of lake bottoms as well as sediment sampling in lakes and on land. Right now, a second field season has come on stream, starting with an in-depth investigation of the Hamana Lake deposits (Oct) for which Ghent University shipped a coring platform (British Antarctic Survey) to Japan. 


In preparation for this year’s fieldwork on Lake Hamana, last year’s data and samples (short gravity cores) were analysed thoroughly in order to retrieve information on prevailing depositional processes, average sedimentation rates and the possible presence and lateral extent of tsunami deposits within the lake basin. Based on that knowledge, a set of sites were selected for collecting long cores (up to 8 m of depth). Hopefully, these long records will shed light on recurrence patterns of tsunamis along the Nankai Trough.


Pouring rain during platform build-up at the Suzuki Marina in Washizu.

Thursday, 8 October 2015

QRN field recce photo diary

Marc, Atsunori, Osamu, Vanessa, Masanobu, Miyairi, Ed, Yusuke and a few others have spent the last few days meeting to discuss the next targets for the onshore field campaign. We spent time travelling along the Shizuoka coast to see some potential new sites and also met up with the QRN lake coring team, who are a week into their campaign on Lake Hamana (More to follow from Evelien Boes soon...). Here are a few photos from the lab and field.

We started the trip checking out some cores stored in Tsukuba, headquarters of the Geological Survey of Japan