Two rock magnetic methods can be used to determine the emplacement temperature of pyroclastic deposits. The first is by looking at the unblocking temperature spectra of the thermoremanent magnetization (TRM) and the second is through the repeatability of thermomagnetic behavior. Chachimbiro volcanic complex is an andesitic-dacitic stratovolcano located at the northern zone of the Ecuadorian volcanic arc. The lateral blast eruption that occurred at 3640-3510 BC originated from a ∼650 m wide and ∼225 m high rhyodacite dome. This satellite lava dome, located ∼6 km to the east of the main vent, erupted, resulting in a large pyroclastic density current (PDC). PDCs are hot mixtures of lithic fragments, gas and pumice, varying in size from fine ash up to metric blocks that descend the flanks of a volcano at great speeds, being the primary cause of death during explosive eruptions. The resulting PDC from this violent laterally directed explosion covered an area of 62 km^2, with the thickest parts of the deposit displaying as much as 15 m. We collected ~63 oriented block samples from 6 locations; their distances varying between 1.8 km to 6.7 km away from the source. Here we present the emplacement temperatures of the Chachimbiro pyroclastic deposits and the potential factors controlling them. Our rock-magnetic results indicate low titanium Ti-magnetite as the main magnetization carrier; maghemite being present in trace amounts. We have recognized that, based on the unblocking analysis of the TRM, the overall temperatures vary from 250 °C to 450 °C depending on the clast size and type. In general, our results suggest a minimum temperature of ~250 °C, with a large portion of the juvenile clasts having temperatures up to about ~450 °C. Furthermore, the analysis and the comparison of the Curie temperature executed in ~30 samples, against the emplacement temperatures obtained through the typical paleomagnetic studies will be presented. This work highlights the usefulness of paleomagnetism and rock magnetism to evaluate the emplacement temperatures of PDCs, thereby allowing to better assess the associated risk.

Geophysical methods are very useful in archeological prospection by providing an inexpensive, non-invasive view of the subsurface, and, helping the archeologists to better target their excavation efforts. Ecuador’s past is very rich, with many archeological sites still unexplored. Manteño culture prevailed in the province of Manabí in a series of large coastal towns and along the river valleys and ridges of the Chongón-Colonche coastal mountains of what is now Ecuador from around 500 CE to 1532 CE. They were one of the last prehistoric cultures and the Inca Empire never conquered them directly, which meant their culture developed independently. Thousands of carefully arranged stone foundation have been documented across the abrupt landscape that has been intentionally modified for large scale agriculture. In this work, we present the results of Electrical Resistivity Tomography (ERT) and magnetometry surveys at the Río Blanco archeological area close to the coastal city of Puerto Lopez. The area includes one of the largest unexcavated archeological remains known in Ecuador. It consists of alluvial terraces modified by the Manteño people scattered with numerous ruins. The archeological structures are often delimited by buried rock blocks that sometimes outcrop in the surface. We made 2 ½ D ERT with dipole-dipole array configuration and ground magnetometry surveys at three locations which were identified earlier by archeologists as buried buildings, with one of them being previously partially excavated. The measurement grid for each structure was designed according to their size. For magnetometry, a base station measurement was taken after finishing each survey line in order to be able to remove diurnal variations from the magnetometry readings. All tested structures showed internal variations within them related to differences in electrical resistivity and magnetic susceptibility. According to our preliminary interpretation, some of these anomalies are from the wall rocks and some suggest the presence of buried objects as well as potential locations of fireplaces. The locations of the buried objects are intended to be later verified by archeological excavation.