Tephra-stratigraphical study of the 1988-1989 eruption of Tokachi-dake Volcano, central Hokkaido

Twenty-three small-scale eruptions took place at Tokachi-dake from December 16, 1988 to March 5, 1989. The pyroclastic fall deposits, ballistic fragments, and pyroclastic surge and flow deposits were dispersed over the flank and leeward areas of the volcano. Because the pyroclasts of each eruption were well-preserved in snow during the winter, the stratigraphy and distribution of these deposits could be studied in detail. The volume of the pyroclastic fall deposits are nearly equal to those of the pyroclastic surge and flow deposits. The total volume of these pyroclasts is estimated to be 7.4×105 m3. Judging from the sequential changes of the volume and composition of the pyroclasts, the characteristic features of the eruption can be summarized as follows: At first, a vent was opened by ejection of altered rock fragments in December, 1988. Then, essential fragments were ejected in January, 1989. Finally the activity level of magma declined and the altered rock fragments content increased again in February to March, 1989

The 1988-1989 explosive eruption of Tokachi-dake, central Hokkaido, Its sequence and mode

On December 16, 1988, after 26 years of dormancy since the last eruption in 1962, Tokachi-dake began to erupt from the 62-II crater. The eruption started with phreatic explosions. Then, on December 19, the activity changed into phreatomagmatic explosions of Vulcanian type and continued intermittently until March 5, 1989. Although the composition of the essential ejecta, mafic andesite, is similar to those of 1926 and 1962 eruptions, the mode of the present eruption is considerably diffrent The present eruption consists of a series of 23 discrete cannon-like explosions, being frequently accompanied with small-scale pyrcclastic surges and flows. The total volume of ejecta amounts to approximately 6×105 m3, of which about 20% is essential ejecta. A complete sequence of events was compiled and distribution maps of the ash-fall, ballistic blocks, and pyroclastic surges and flows were drawn for each of the larger eruptions. The pyrrolastic surges and flows of the present eruption were small scale, low temperature pyroclastic flows, rich in accessory clasts and unaccompanied by sector collapse. Therefore, the sudden melting of snow causing disastrous mudflows, as in the case of the 1926 eruption, fortunately did not occur

Surgical exploration after overlapping stents for a ruptured blood blister-like aneurysm: Direct observation of the stent struts through the vessel wall defect and its clinical implications

Background: Blood blister-like aneurysms (BBAs) are a rare but clinically important cause of subarachnoid hemorrhage. Although regrowth or repeat rupture can occur following reconstructive endovascular treatment of BBAs, there is currently a lack of studies reporting the surgical exploration of BBAs after endovascular management. Herein, we present the first case report of a ruptured BBA treated with reconstructive endovascular treatment followed by surgical exploration. Case Presentation: A 42-year-old woman with subarachnoid hemorrhage was found to have the following: a saccular aneurysm of the lateral wall of the right supraclinoid internal carotid artery (ICA); and irregular vessel wall of the anterior wall of the right supraclinoid ICA on angiography. Based on intraoperative findings, the patient was diagnosed with a ruptured BBA of the right ICA. She underwent coating of the dissected ICA followed by overlapping stents; however, angiography showed rapid regrowth of the aneurysm. After high-flow bypass, surgical exploration was performed under proximal control of the cervical ICA. The deployed stent was directly observed through a vessel wall defect of the anterior wall which was consistent with angiographical irregular vessel wall. There was a clear positional discrepancy between angiographical base of the aneurysm and intraoperative laceration site. Conclusions: Surgical exploration indicates there is a potential risk of regrowth and/or repeat rupture of BBAs until the stent is fully endothelialized. Moreover, stent should be deployed to ensure that the irregular vessel wall is included when reconstructive endovascular treatment is employed for ruptured BBAs associated with irregular vessel wall

Fossil Rootless Fumaroles in the Noboribetsu Pumice Flow Deposits and Their Alteration Products in the Noboribetsu Formation, Kuttara Volcano, Southwestern Hokkaido, Japan

Many fossil rootless fumaroles are found in the upper unwelded facies of the Noboribetsu Pumice Flow Deposits, which are distributed around the Kuttara Caldera, SW Hokkaido. Rootless crater pits immediately above the fumaroles are filled by pumice, scoria, ash, and mud of the Noboribetsu Formation overlying the Noboribetsu Pumice Flow Deposits. Alteration due to the fumarolic action clearly extends into the Noboribetsu Formation. The origin of the Noboribetsu Formation is suggested to be a base surge deposit based on its distribution and lithological characteristics

Frontal Encephalocele Plus Epilepsy: A Case Report and Review of the Literature

An encephalocele is a pathological brain herniation caused by osseous dural defects. Encephaloceles are known to be regions of epileptogenic foci. We describe the case of a 44-year-old woman with refractory epilepsy associated with a frontal skull base encephalocele. Epilepsy surgery for encephalocele resection was performed; however, the epilepsy was refractory. A second epilepsy surgery for frontal lobectomy using intraoperative electroencephalography was required to achieve adequate seizure control. Previous reports have shown that only encephalocele resection can result in good seizure control, and refractory epilepsy due to frontal lobe encephalocele has rarely been reported. To the best of our knowledge, this is the first report of frontal encephalocele plus epilepsy in which good seizure control using only encephalocele resection was difficult to achieve. Herein, we describe the possible mechanisms of encephalocele plus epilepsy and the surgical strategy for refractory epilepsy with encephalocele, including a literature review