Application of tephra volume models to ejecta volumes from subsurface explosion experiments
Deposit volume is a critical factor for reconstructing an explosive eruption. Volume estimate models typically used for large Plinian deposits have been adapted and improved repeatedly over the last few decades. Less work has been done to refine a method for estimating the volume from smaller deposits produced by discrete phreatic and phreatomagmatic explosions. The characterization of the volume and distribution of deposits is required to quantify the physical hazards presented by different explosion types and develop appropriate models of future eruptions. Six classic tephra volume models were assessed using a dataset from subsurface explosion experiments. The models typically did a poor job modelling the volume of proximal deposits as a component of total deposit volume of discrete explosion deposits. Models reproduced medial and distal deposit volumes with greater success, particularly the Exponential model and a more recent Linear Regression model. It is therefore recommended, when possible, to use digital elevation models produced from GPS or laser-based methods to characterize proximal deposits separately and to use tephra volume estimates for medial and distal deposits. Additionally, this dataset enabled the comparison of ejecta volumes with crater diameters and highlighted that this relationship only holds for simple crater scenarios without any lateral vent migration, collapse or erosion of the crater under study. The assessment and improvement of these methods are required to ensure accurate deposit volumes as they serve as one of the most important inputs to hazard assessments and numerical models.
Relationship between crater size and ejecta volume of recent magmatic and phreato‐magmatic eruptions: Implications for energy partitioning
Relationships between crater diameter (D in meters) and ejecta volume (V in cubic meters) of recent magmatic and phreato‐magmatic eruptions are expressed as D=0.11 V0.42, and D=0.97 V0.36, respectively. Crater diameters of phreato‐magmatic eruptions are ca. 2–5 times larger than those of magmatic eruptions of similar ejecta volume, suggesting that magma‐water interaction in phreato‐magmatic eruptions generated mechanical energies of crater formation 1–2 orders of magnitude larger than equivalent‐volume magmatic eruptions. The conversion ratio of thermal energy to kinetic energy in phreato‐magmatic eruptions is estimated to be 0.7–10 percent, which is in accord with the presently available data of laboratory experiments on melt‐water interaction [Wohletz and McQueen, 1984].
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125