This is a new technique where we collect samples from large tsunami boulders (recently from Cape Verde) that were quarried and rotated during the tsunami. Afterwards they slowly acquire a viscous remagnetization whose intensity/blocking temperature increases over time. By measuring this viscous remagnetization, we can calculate the age of the tsunami.
The method has previously been successful to date glacial flood boulders in Iceland (photo) and was featured in the Earth Magazine.
It involves collecting oriented samples of various large (meters) boulders that were deposited by the flood. They are then demagnetized using continuous thermal demagnetization which allows an exceptionally high temperature resolution to determine the unblocking temperature of post-flood VRM.
Afterwards, a serious of viscosity experiments is performed to empirically determine the rate at which the particular sample acquires a VRM. This approach yield order-of-magnitude age estimates of the flood, and has been shown for the first time to be statistically significant and reliable.
As many geological events such as floods (but also landslides and others) cannot always be dated by traditional methods such as radiometric dating, VRM dating may one day become an important tool for natural hazard risk assessments
Recently we also went to Cape Verde to test this method on ancient mega-tsunamis.
The details of the method can be found in:
- Berndt, T., & Muxworthy, A. R. (2017). Dating Icelandic glacial floods using a new viscous remanent magnetization protocol. Geology, 45(4), 339–342. https://doi.org/10.1130/G38600.1