Pliny the Younger, a Roman writer who published a detailed description of the AD 79 eruption, including his uncle's death. On occasion, eruptions from Vesuvius have been so large that the whole of southern Europe has been blanketed by ash; in 472 and 1631, Vesuvian ash fell on Constantinople (Istanbul), over away. A few times since 1944, landslides in the crater have raised clouds of ash dust, raising false alarms of an eruption. Since 1750, seven of the eruptions of Vesuvius have had durations of more than five years; only Mount Etna has had as many long-duration eruptions in the last 270 years. The two most recent eruptions of Vesuvius (1875–1906 and 1913–1944) each lasted more than 30 years. Vesuvius is still regarded as an active volcano, although its current activity produces little more than sulfur-rich steam from vents at the bottom and walls of the crater. Layers of lava, ash, scoria and pumice make up the volcanic peak. Their mineralogy is variable, but generally silica-undersaturated and rich in potassium, with phonolite produced in the more explosive eruptions (e.g. the eruption in 1631 displaying a complete stratigraphic and petrographic description: phonolite was firstly erupted, followed by a tephritic phonolite and finally a phonolitic tephrite). Volcanic explosivity index According to the Smithsonian Institution's Global Volcanism Program, Vesuvius has had 54 confirmed eruptions during the Holocene Epoch (the last 11,700 years). A volcanic explosivity index (VEI) has been assigned to all but one of these eruptions. Before AD 79 Scientific knowledge of the geologic history of Vesuvius comes from core samples taken from a plus borehole on the flanks of the volcano, extending into Mesozoic rock. Cores were dated by potassium–argon and argon–argon dating. The area has been subject to volcanic activity for at least 400,000 years; the lowest layer of eruption material from the Somma caldera lies on top of the 40,000-year‑old Campanian ignimbrite produced by the Campi Flegrei complex. The volcanic complex stands on a large, sedimentary plain. 25,000 years ago: Vesuvius started forming in the Codola Plinian eruption. Vesuvius was then built up by a series of lava flows, with some smaller explosive eruptions interspersed between them. By this time, the volcano was 2,000 meters (6,560 feet) tall, with the summit being 500 meters (1,640 feet) east of the current summit. About 19,000 years ago: the style of eruption changed to a sequence of large explosive and caldera-forming Plinian