GEOL 3500 - Earthquakes & Volcanoes
Figures F-1.6, F-1.9, F-2.2, F-2.3, F-2.6, F-2.13, F-2.15, F-2.22
1. What is the difference between science and religion (or math, or philosophy)? How about between science and the so-called social disciplines?
2. List the basic steps followed in the scientific procedure of multiple hypotheses.
3. Briefly describe the three revolutions in geology (uniformitarianism, geologic time, and global/plate tectonics.
4. How does the book define volcanism? (Key words are thermal processes, and solid, liquid and gaseous products).
5. Explain what is wrong with the popular conception that a volcano is a burning mountain from the top of which issue smoke and fire.
6. What is a volcanic system? Draw a diagram of one (one of my favorite exam questions!)
7. What are the five sources of internal thermal energy in the Earth? Which of them remain active to date?
8. What is magma?
9. Where do magmas come from?
10. What are the three families of rocks? How do they form?
11. What is an intrusive or plutonic rock?
12. What is a volcanic rock?
13. What is a volcanic glass? How do they form?
14. What is a mineral? (You need to remember the formal definition given in the book)
15. What are the seven common minerals found in volcanic rocks?
16. How do glasses and minerals differ?
17. How are rhyolites, andesites and basalts distinguished in terms of silica content?
18. Fill up the following table with high and low for each category
Basaltic magma Rhyolitic magma
SiO2 content _____________ _____________
Density _____________ _____________
Viscosity _____________ _____________
Temperature _____________ _____________
Volatile content _____________ _____________
Tendency to form lavas _____________ _____________
Tendency to form pyroclastics_____________ _____________
19. What happens when magma quenches suddenly?
20. What happens when magma cools slowly?
21. Draw a diagram of the internal structure of the Earth. On one half label the compositional layers, and on the other the mechanical layers (one of my favorite exam questions).
22. How are the continental and oceanic crusts different in terms of (1) composition, (2) age, (3) density?
23. What is the evidence given by the book in support of seafloor spreading and plate tectonics?
24. Describe the three major types of plate boundaries, give an example of each, and point out to which of them is volcanic activity associated.
25. What is the Pacific Rim of Fire? Name 10 volcanoes within it.
26. What is a continental rift?. Name three continental rifts.
27. According to the book, how is the base of the lithosphere determined? (Key word: Geotherm).
28. What is an ophiolite?
29. Draw a schematic section through typical oceanic crust. (Fig. 2.15)
30. Draw a schematic section through a mid-ocean ridge. (Fig. 2.18)
31. Convection is believed by many to be the driving force of plate tectonics. Draw a schematic section showing how this explains the development of mid-ocean ridges and subduction zones.
32. The book gives an alternative hypothesis, and suggests that pull by the subducting slab might be the driving force. Illustrate this hypothesis with a simple diagram.
33. Can the slab-pull hypothesis explain the current spreading of the Atlantic?
34. What is an island arc? What types of volcanic rocks are found in them?
35. Give five examples of island arcs.
36. What is the Benioff zone?
37. What is a hot spot? Illustrate the idea of a mantle diapir with the help of a diagram.
38. Why do the islands of the Hawaiian archipelago become progressively older to the northwest?
39. Why is there a dog-leg between the Hawaiian archipelago and the Emperor sea mount chain?
40. Which direction is the Pacific plate moving?
41. Give two examples of continental hot spots.
42. Give two examples of oceanic hot spots.
43. What are continental flood basalts? Give four examples of continental flood basalts.
44. What relation is there between continental rifting and continental flood basalts.
45. Basaltic magma is only generated by partial melting of the mantle (5 to 20% by volume). Which conditions, or processes, can lead to partial melting of the mantle?
46. How do rhyolitic magmas differ from basaltic magmas in terms of:
SiO2 content
Al2O3 content
Na2O + K2O content
CaO content
FeO content
MgO content
(Note: Remember that andesites tend to be somewhere in between.)
47. Why is it said that magma is a polymerized melt?
48. What is polymerization and why does it happen in silicate melts?
49. How does polymerization affect the viscosity of a magma?
50. Why do magmas crystallize over a range of temperatures, rather than at a single temperature like ice?
51. What is the solidus? What is the liquidus?
52. How does the melting temperature of a dry rock vary with pressure?
53. How does the melting temperature of a wet rock vary with pressure?
54. What are phenocrysts? What do they tell us about the cooling history of a volcanic rock?
55. What are the common volatile compounds found in solution in magmas?
56. How does the solubility of a volatile compound, such as H2O, change as a function of pressure? As a function of temperature?
57. How would you explain the fact that rhyolitic magmas contain much more dissolved H2O (up to 5 wt%) than basaltic magmas (usually less than 1%)?
58. Why are the early stages of eruptions more explosive than later stages?
59. What is viscosity?
60. How does viscosity change as a function of temperature, water content, and SiO2 content of a melt?
61. Come up with one example each of Newtonian, pseudo-plastic, and Bingham fluids.
62. What is vesiculation?
63. Why do vesicles form in a magma? (Concentrate on the so-called first boiling process).
64. Write down the rough chain of cause and effect given in the summary of Chapter 5. What part of this chain don't you understand?
Figure 6.4
65. What is the difference between effusive and explosive eruptions?
66. What determined whether an eruption will be effusive or explosive?
67. What is the difference between magmatic and phreatomagmatic eruptions?
68. What is the difference between a central vent and a fissure eruption?
69. What is an eruption column?
70. What is a hawaiian eruption? Describe it in terms of magma composition, explosivity, and typical products.
71. What is a strombolian eruption? Describe it in terms of magma composition, explosivity, and typical products.
72. What is a vulcanian eruption? Describe it in terms of magma composition, explosivity, and typical products.
73. What is a Plinian eruption? (Use the formal definition I gave you in class)? List its characteristic magma composition, explosivity, and typical products.
74. What is a peléean eruption? Describe it in terms of magma composition, explosivity, and typical products.
75. What is a surtseyan eruption? Describe it in terms of magma composition, explosivity, and typical products.
76. List four scenarios that could lead to a phreatomagmatic eruption.
77. What is a jokulhlaup?
78. How does the mantle rise over hot spots?
79. How do basaltic magmas rise through the mantle?
80. How do basaltic magmas rise through the crust?
81. Rhyolitic magma is too cool and viscous to easily move through a dike in any large amounts. Knowing this, what explanation has been suggested for the generation and rise of large volumes of rhyolitic magma?
82. How do diatremes form?
83. In summary, in which three ways do magmas rise from their sources to the high level reservoirs that feed volcanoes?
84. Draw a magma chamber zoned from basaltic to rhyolitic levels. In your diagram indicate typical temperature gradients, water content gradients, and crystal content gradients.
85. Given the magma chamber from the previous question, in what order will be the magmas erupted in the course of a major eruption? Draw a schematic figure of the deposit that such an eruption would form.
86. What could have triggered the major eruption of the previous question?
87. Given the major eruption of question 85, what might bring it to a halt? (I can think of at least three possible reasons).
88. Describe the process of formation of a lava tube.
89. Again, what is viscosity? What is yield strength?
90. Why do levees form along the sides of lava flows?
91. Contrast the characteristic thicknesses and lengths of rhyolitic, andesitic, and basaltic lava flows.
92. What are the critical factors that control the lengths of lava flows?
93. What is a compound flow? What is a simple lava flows?
94. What is meant by the term tube-fed flow?
95. What is meant by the term surface-fed flow?
96. What are tumuli? Hornitos? Lava deltas? Littoral cones?
97. Arranged by whether they are submarine or subaerial, and by composition, what are the typical flow morphologies for rhyolites, andesites, and basalts?
98. What is a coulée? What is a torta? What is a peléean dome?
Figures 8.2, 8.4, 8.7, 8.9, 8.14
99. What are the three stages involved in an explosive volcanic eruption?
100. What drives the rise of eruption columns? Put in another words, why is mass eruption rate the critical factor in the rise of an eruptive column?
101. Again, what is a strombolian eruption? What is a vulcanian eruption?
102. What factors control the muzzle velocities of eruption columns?
103. Draw a diagram of a Plinian eruption column. Label the layers of the atmosphere. Assume wind blows from the left (one of my favorite exam questions).
104. In which three parts or regions can a volcanic column be divided?
105. Define troposphere, stratosphere, tropopause. At what altitude is the tropopause normally located?
106. What is terminal fall velocity?
107. What falls faster, a ton of feathers or a ton of lead? Why?
108. What falls faster, a pound of lead or a ton of lead? Why?
109. What falls faster, an ounce of feathers or an ounce of lead? Why?
100. Walking away from a volcano like Mt. St. Helens, what would you expect to see happen to the size of pumice fragments? What about the thickness of the pumice deposit?
111. What is an isopleth? What would the pumice-fragment-size isopleths of Mt. St. Helens look like? How about the thickness isopleths?
112. List two practical applications of theoretical analysis of eruption columns.
Figures 9.3, 10.1, 10.2, 10.6, 10.10, 10.19, 10.31
113. What is tephra? What is a tuff?
114. How is tephra classified in terms of size? In terms of origin?
115. What conditions in an eruption column lead to the formation of air-fall deposits?
116. What conditions in an eruption column lead to the formation of pumice flows?
117. As used in chapter 9, what is the difference between an isopach map and an isopleth map?
118. What is sorting?
119. Pyroclastic flow deposits can be divided in four types: Pumice flows or ignimbrites, nuées ardentes or block-and-ash flows, pyroclastic surges, and lahars. What are the characteristics of each in terms of: (1) mode of formation, (2) mechanism of mobility (that is, what allows them to move so readily?), (3) relation to topography, (4) nature of the deposits (do they have pumice or not?, are they stratified or chaotic?, are they welded or not?), (5) extent of the deposits.
120. How are pumice flows formed? (Page 210, first paragraph)
121. How do pumice flows, made of solid lumps of pumice and shards, attain their spectacular mobility? (Key words: Fluidization, momentum transfer)
122. Pumice flows are said to be semi-fluidized mixtures. What is meant by fluidization? What is a fluidized bed?
123. Formally, what is an ignimbrite?
124. Contrast air-fall tuffs with ignimbrites in terms of (a) relation to topography, (b) dispersal, (c) sorting (i.e., range in sizes of tephra at any given location), (d) welding, (e) volume.
125. What is the difference between a pumice flow and a pyroclastic surge?
126. Describe three characteristics that would allow you to distinguish and ignimbrite from a lahar.
127. What conditions need to come together for a lahar to form? In other words, what ingredients are necessary for a lahar to form? (One of my favorite exam questions)
128. How do volcanic eruptions trigger lahars?
129. What other, non-volcanic, phenomena can trigger lahars?
130. What is a monogenetic volcano? What is a characteristic lifespan for a monogenetic volcano? Why are their lifespans so short?
131. Arranged by magma composition, summarize in a table the main types of monogenetic volcanoes.
132. What are the main characteristics of scoria cones?
133. What are the main characteristics of maars?
134. What are the main characteristics of domes?
135. What is a polygenetic volcano?
136. Arranged by magma composition, summarize in a table the main types of polygenetic volcanoes. Include typical lifespans for each major type.
137. Describe the stages in the evolution of oceanic island volcanoes.
138. Speaking of volcanic islands in the shield-building stage, like Hawaii, why is it that volcanic tremor, earthquake swarms, and summit deflation are indicative of apending eruption.
139. Why do oceanic shields develop rift zones?
140. What types of submarine landslides are common in oceanic island volcanoes?
141. Describe the major stages of development of andesitic stratovolcanoes.
142. Draw a diagram of an andesitic stratovolcano, showing proximal, medial, and distal facies.
143. How do calderas form?
144. What are the major stages of development of resurgent cauldrons?
145. Give examples of collapse calderas in California, Oregon, Wyoming, New Mexico and Alaska.
146. How do volcanic eruptions affect climate?
147. Do all volcanic eruptions affect climate?
148. What conditions are favorable for the formation of a geothermal reservoir?
149. How is electricity generated in geothermal fields like The Geysers?
150. What uses do medium-temperature geothermal resources have?
151. What are the hazards associated with lahars?
152. What are the hazards associated with lava flows?
153. What are the hazards associated with ignimbrites?
154. What are the hazards associated with air-fall tuffs?
155. What steps can be taken to alleviate volcanic risk?
156. What are the advantages and disadvantages of engineering solutions in hazard control? Give examples.
157. Is insurance a good measure to alleviate volcanic risk? Why or why not?
158. What is the formal definition of risk?
159. How is the concept of risk used for planning?
Boxes and tables: Brumbaugh book: Box 1.1, Box 2.1, Table 2.1, Box 2.2, Box 2.6 (a favorite exam question), Box 2.8, Box 3.2
Figures: Brumbaugh book: Figures 1.9, 2.17, 2.18, 3.3, 3.5 (a favorite exam question), 3.19
Chapter 1.
160. What is an elastic wave?
161. What is an earthquake?
162. What causes earthquakes?
163. Explain the elastic rebound theory of earthquake generation. (Long, detailed answer)
164. What is the difference between elastic, plastic and brittle deformation?
Chapter 2.
165. What is intensity? How is it measured?
166. What is magnitude? How is it measured?
167. What is a seismograph? What is an accelerograph?
168. What is the principle of operation of a seismograph?
169. Given a wave, define wavelength, amplitude, and frequency (Box 2.6)
170. Given a seismograph record, label the arrival of the P and S waves.
171. Which one is faster, a P or an S wave?
172. What is the difference between body and surface waves?
173. What are the two types of body waves?
174. What are the two common types of surface waves?
175. What differences are there between P and S waves?
176. What differences are there between S and Love waves?
177. What differences are there between Love and Raleyigh waves?
Chapter 3.
178. What is a fault?
179. Define a normal fault. Under what stress regime do normal faults form?
180. Define a reverse fault. Define a thrust fault. Under what stress regime do these faults form?
181. Define a right-lateral strike-slip fault. Define a left-lateral strike-slip fault. Under what stress regime do strike-slip faults form?
182. What is an active fault? What land features do geologists use to tell whether a fault is active or not?
183. Where do transform faults form? What are their characteristics?
184. Be able to label on a map the main active faults of California. (Class handout)
185. What is a seismic gap?
186. What effect does water have on the brittle deformation of rocks?
187. Explain the relation between deep injection of liquid wastes at the Rocky Mountains Arsenal and the Denver earthquake swarms of 1962. What explanation was given for this relation.
188. How can water be used to release stored elastic energy?
189. Would it be wise to use water injection to release the elastic strain in the San Andreas fault?
Boxes: Brumbaugh book: 4.1, 6.1, 6.2
Figures: Brumbaugh book: 4.1, 4.2, 4.4, 5.8, 6.7
Chapter 4.
190. Define focus, hypocenter, epicenter
191. How are the epicenters of earthquakes located?
192. What is magnitude? How is it measured? (I want the long, detailed answer this time).
193. What is the relation between magnitude and energy released?
194. What is seismic moment?
195. How is the concept of seismic moment used to estimate moment magnitude?
196. How is moment magnitude estimated for historic earthquakes?
Chapter 5. READ THIS CHAPTER LIGHTLY AND TRY NOT TO GET FRUSTRATED!
197. What is a fault-plane solution?
198. Why does the author claim it is a powerful and useful tool?
199. Given a fault plane (e.g., Fig. 5.19 and Fig 10.2), where do main shocks usually occur? Why?
200. Where do aftershocks occur? Why?
Chapter 6.
201. List the evidence given in the book in support of the theory of plate tectonics. Be thorough!
202. Summarize Arthur Holmes' idea that convection is the key mechanism in the spreading of the ocean floors.
203. What is a magnetic reversal?
204. What is paleomagnetism, and how was it used to confirm the process of seafloor spreading.
205. How are interplate earthquakes generated?
206. What is the Wadati-Benioff zone?
207. Where do shallow-focus earthquakes occur? What is a shallow-focus earthquake, anyway?
208. Where do intermediate- and deep-focus earthquakes occur? What is considered intermediate, and what is considered deep?
Boxes: Brumbaugh book: 10.1
Figures: Brumbaugh book: 7.2, 7.3, 7.5, 7.8, 7.9, 7.13, 8.3, 10.7, 10.10
Chapter 7.
209. With a simple diagram, explain the principle of wave reflection.
210. With a simple diagram, explain the principle of wave refraction. Give special attention to the rigidity of the two media, and to the differences in velocity between P and S waves.
211. State Snell's law of wave refraction. Make sure you understand what all the terms refer to.
212. How was the internal structure of the Earth determined? (See Fig. 7.9)
213. Define: Inner core, outer core, mantle, crust, astenosphere, lithosphere.
214. What is seismic tomography, and how was it used to study the magma chamber of the Long Valley caldera?
Chapters 8 and 9.
215. What were the major causes of death in the San Francisco earthquake?
216. What is a tsunami? How are they generated?
217. What is a seiche?
218. What is liquefaction? What conditions may lead to liquefaction?
219. Why is liquefaction of concern?
220. What can be done to alleviate liquefaction risks?
221. What hazards are posed to dams by earthquakes?
222. Why was the 1985 Mexico City earthquake so devastating?
223. List the main earthquake hazards (your list should include 8 to 10 line items based on the examples given).
224. How are intraplate earthquakes generated? (Discussion not in the book)
225. Where in the United States are intraplate earthquakes a matter of concern?
Chapter 10.
226. What is a seismic gap, and what implications does it have for earthquake prediction?
227. Explain the dilatant-diffusion theory (Figure 10.7), and what earthquake prediction approaches has it lead to?
228. What approaches are being currently investigated as possible earthquake prediction tools? Organize your answer in form of a list, and make sure you know what each item is all about.
229. Discuss the economic and societal implications of earthquake prediction.
230. How are the odds of an earthquake calculated in terms of:
- Location
- Timing (see Box 10.1)
- Size or magnitude
231. What type of impacts would the prediction of a large earthquake have in the Los Angeles area?
Chapter 11.
232. List the measures that San Francisco residents can take to prepare for the Big One.
233. List the things to keep in mind if you are caught inside a building during an earthquake.
234. List the things to keep in mind shortly after an earthquake.
Chapter 12.
235. From the standpoint of hazard to life and property which is more important, intensity or magnitude?
236. Why do newspapers and news casts ram down out throats the magnitude of an earthquake, but say nothing about its intensity? What does this tell you about the role of the press?
237. Define peak horizontal acceleration? Define repeatable horizontal acceleration?
238. Describe the phenomenon of attenuation of seismic waves with distance.
239. Do seismic waves attenuate faster in solid rock or in loose sediment?
240. Form the standpoint of seismic risk, which faults are most important for Central Valley residents?
241. Why is horizontal acceleration important for building design?
242. What does the Uniform Building Code says about building in the Central Valley of California? In other words, what do you, the home owner, need to ask your building contractor to look at during the design stage of your dream home.
243. Why are we particularly concerned about liquefaction in the Central Valley?
Discussions not in the book.
244. How is the concept of risk used for policy decisions?
245. What steps can be taken to alleviate seismic risk?
246. What are the advantages and disadvantages of engineering solutions in hazard control? Give examples.
247. How about soft solutions like zoning or upgraded building codes? List specific examples of soft solutions.
248. Is insurance a good measure to alleviate seismic risk? Why or why not?
249. What is an Alquist-Priolo fault hazard zone?
250. How are the concepts of operating basis earthquake and safe-shutdown earthquake used in the design of hospitals, schools, and critical lifeline structures (e.g., bridges, power lines)?
251. What is acceptable risk?
GEOL 3810 - Hydrogeology
Figures 1.3 (one of my favorite exam questions!), 1.4
Homework: Chapter 1 problems 1, 5, 9, 13
1. What is hydrology?
2. What is hydrogeology?
3. Why is an abundant supply of good quality water important for human settlements.
4. Draw and label a sketch of the hydrologic cycle. Include the percentages of water held in the oceans, the atmosphere, glaciers, groundwater, lakes and rivers.
5. What happens to precipitation once it has fallen on the land? (Long, detailed answer)
6. Where does the water that flows in rivers come from?
7. State the hydrologic equation (or law of mass conservation).
8. Define: Surface drainage basin, groundwater basin, vadose zone, zone of saturation, water table.
9. List the hydrologic inputs to an area like the San Gabriel Basin.
10. List the hydrologic outputs to an area.
11. List the different types of change in water storage in an area.
12. What does a hydrogeologist do? (Long, detailed answer).
13. What is an ASTM standard?
14. What are the dimensions of: Length, area, volume, velocity, discharge (volume per unit time)?
15. Make an Excel spreadsheet program (print the formulas so I can see that you got it right) to convert measurements in feet to inches, yards, miles, millimeters, centimeters, meters and kilometers
16. Make an Excel spreadsheet program (print the formulas so I can see that you got it right) to convert measurements from:
miles to feet
square miles to square feet
square miles to acres
acres to square feet
acres to square meters
gallons to cubic feet
cubic feet to acre-foot
cubic feet to cubic yards
cubic feet to cubic meters
cubic meters to liters
meters to feet
inches to centimeters
seconds to minutes to hours to days to years
feet/day to cm/sec
Figures 2.1, 2.2, 2.5, 2.6, 2.9, 2.10, 2.16 (a favorite exam question), 2.25,
Homework: Chapter 1 problems 3, 5, 13, 17
17. What is the difference between climate and weather.
18. Sketch the climatic zones of California.
19. Define: Absolute humidity, saturation humidity, relative humidity, dew point.
20. What leads to precipitation events?
21. How does topography affect precipitation?
22. How is precipitation measured?
23. Total annual precipitation is a convenient way of distinguishing climatic zones. In contrast, individual precipitation events are hard to forecast, so we normally use probability. What is the meaning of the expression "25-year 6-hour rainfall".
24. What would be a bigger event, the 2-year 24-hour rainfall or the 25-year 24-hour rainfall?
25. What would be a bigger event, the 25-year 6-hour rainfall or the 25-year 24-hour rainfall?
26. What is the effective depth of precipitation?
27. What is the effective depth of precipitation for a snowfall event?
28. Contrast the advantages and disadvantages of isoyethal and Thiessen polygon methods for estimating effective precipitation.
29. Again, what happens to precipitation once it has fallen on the land? (Long, detailed answer)
30. What conditions determine the initial infiltration capacity of a soil?
31. How does infiltration capacity change with time during a precipitation event?
32. How is potential evaporation normally measured? How do we apply these values to calculate actual evaporation?
33. Define: Transpiration, wilting point, evapotranspiration (ET), potential ET, and actual ET.
34. How is evapotranspiration measured?
35. What is a lysimeter?
36. Define: Horton overland flow, interflow, baseflow, baseflow recession, effluent (gaining) streams, influent (loosing) streams.
37. State the rational equation, and describe each of its terms (include dimensions and typical units).
38. What is the suggested range of runoff coefficients for "unimproved" ground (98% of the ground falls in this category)? Where do these numbers come from?
39. Speaking of surface streams, what is discharge? How is it measured? What are its typical dimensions and units?
40. State Manning's equation, and describe each of its terms (include dimensions and typical units). Write down the typical values of the Manning roughness coefficient.
107. Arrange the following in terms of their importance as sources of water supply: Lakes and reservoirs, groundwater, rivers
110. What is discharge? In what units is it measured?
111. What happens to the cross-section of a stream when discharge increases? What happens when discharge decreases?
112. What is a flood plain?
113. What causes floods?
114. How can we mitigate flood hazards?
115. How is groundwater "stored" underground? (In underground rivers or water veins?)
116. Define zone of saturation, zone of aeration, water table.
117. What is the general shape of the water table?
118. What is porosity?
119. Why is it said that granites have a low primary porosity but can have high secondary porosity?
120. What is permeability?
121. What is an aquitard? What types of rocks form good aquitards?
122. What is an aquifer? What types of rocks form good aquifers?
123. What controls the flow of groundwater? In other words, which way does groundwater flow?
124. What is the hydraulic gradient?
125. Write down Darcy's law. Know what each term means.
126. How fast does groundwater move?
127. How do springs form?
128. What is a perched water table?
129. What happens to the water table when a well is pumped?
130. How do geologists look for groundwater in an area like the Central Valley?
131. What is an artesian well? (Formal definition)
132. What conditions must be met to have a confined aquifer?
133. What is an unconfined aquifer?
134. Is the Central Valley aquifer confined or unconfined? Draw a cross section of the groundwater basin of the Central Valley.
135 Should we be pumping like there is no tomorrow out of the Central Valley aquifer, or is this a resource that we should leave alone for future generations?
136. How can groundwater extraction trigger seawater intrusion?
137. Where in California has seawater intrusion affected groundwater basins?
138. What human activities can lead to pollution of groundwater?
139. What can we do about it?
140. The Pala indians, who live in the valley of the San Luis Rey River near Gregory Canyon, want to create a water district to mine groundwater and sell it to the San Diego County Water Authority (alas, the San Luis Rey River water is all apportioned, so they cannot pump water out of the river for this purpose). They have invited you to bid for the water exploration program. What would you propose to do for them?
Updated: July 12, 2023